Image-forming member for electrophotography

ABSTRACT

Image-forming member for electrophotography comprising a charge generation layer composed of hydrogenated amorphous silicon.

This is a continuation of application Ser. No. 763,214 now U.S. Pat. No.4,613,558, filed Aug. 7, 1985, which is a division of application Ser.No. 565,191 filed Dec. 23, 1983 now U.S. Pat. No. 4,557,990, which is adivision of application Ser. No. 269,846 filed June 3, 1981, now U.S.Pat. No. 4,461,819, which is a continuation of application Ser. No.016,986, filed Mar. 2, 1979, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an image-forming member for electrophotographywhich is used to form images by utilizing electromagnetic wave such aslight including for example, ultraviolet ray, visible ray, infrared ray,x ray, gamma ray and the like.

2. Description of the Prior Art

Heretofore, there have been used inorganic photoconductive materialssuch as Se, CdS, ZnO and the like and organic photoconductive materialssuch as poly-N-vinylcarbazole, trinitrofluorenone and the like as aphotoconductive material for photoconductive layers ofelectrophotographic image-forming members.

However, they are suffering from various drawbacks. For example, sinceSe has only a narrow spectral sensitivity range with respect to forexample visible light, its spectral sensitivity is widened byincorporation of Te or As. As a result, an image-forming member of Setype containing Te or As is improved in its spectral sensitivity range,but its light fatigue is increased. On account of this, when the same,one original is to be continuously copied repeatedly, the density of thecopied images is inadvantageously decreased, and fog occurs in thebackground of the image, and further undesirable ghost phenomenon takesplace.

In addition, Se, As and Te are extremely harmful to man. Therefore, whenan image-forming member is prepared, it is necessary to use a speciallydesigned apparatus which can avoid contact between man and those harmfulsubstances. Further, after preparation of an image-forming member havingsuch a photoconductive layer formed of those substances, if thephotoconductive layer is partly exposed, part of such layer is scrapedoff during the cleaning treatment for the image-forming member andmingles with developer, is scattered in copying machine and contaminatescopied image, which causes contact between man and the harmfulsubstances.

When Se photoconductive layer is subjected to a continuous andrepetitive corona discharge, the electric properties are frequentlydeteriorated since the surface portion of such layer is crystallized oroxidized.

Se photoconductive layer may be formed in an amorphous state so as tohave a high dark resistance, but crystallization of Se occurs at atemperature as low as about 65° C. so that the amorphous Sephotoconductive layer is easily crystallized during handling, forexample, at ambient temperature or by friction heat generated by rubbingwith other members during image forming steps, and the dark resistanceis lowered.

On the other hand, as for an electrophotographic image-forming member ofbinder type using ZnO, CdS and as photoconductive layer-constitutingmaterial, formation of the photoconductive layer having the desiredproperties is difficult because such layer consists of photoconductivematerial and binder resin and the former must be uniformly dispersedinto the latter. Therefore, parameters for determining the electricaland photoconductive, or physical and chemical properties of thephotoconductive layer must be carefully controlled in forming thedesired photoconductive layer. Accordingly, the image-forming memberhaving such photoconductive layer is not suitable for the massproduction.

The binder type photoconductive layer is so porous that it is adverselyaffected by humidity and its electric properties are deteriorated whenused at a high humidity, which results in formation of images havingpoor quality. Further, developer is allowed to enter into thephotoconductive layer because of the porosity, which results in loweringrelease property and cleaning property. In particular, when the useddeveloper is a liquid developer, the developer penetrates into thephotoconductive layer so that the above disadvantages are enhanced.

CdS itself is poisonous to man. Therefore, attention should be paid soas to avoid contact with CdS and dispersion thereof.

ZnO photoconductive layer of binder type has low photosensitivity andnarrow spectral sensitivity range and exhibits remarkable light fatigueand slow photoresponse.

Electrophotographic image-forming members comprising an organicphotoconductive material such as poly-N-vinylcarbazole,trinitrofluorenone and the like have such drawbacks that thephotosensitivity is low and the spectral sensitivity range with respectto for example the visible light region is narrow and in a shorter wavelength region.

In order to solve the above mentioned problems, the present inventorshave researched amorphous silicon (hereinafter called "a-Si") andsucceeded in obtaining an electrophotographic photosensitive member freefrom these drawbacks.

Since electric and optical properties of a-Si film vary depending uponthe manufacturing processes and manufacturing conditions and thereproducibility is very poor (Journal of Electrochemical Society, Vol.116, No. 1, pp 77-81. January 1969). For example, a-Si film by vacuumevaporation or sputtering contains a lot of defects such as voids sothat the electrical and optical properties are adversely affected to agreat extent. Therefore, a-Si had not been studied for a long time.However, in 1976 success of producing p-n junction of a-Si was reported(Applied Physics Letters, Vol. 28, No. 2, pp. 105-107, Jan. 15, 1976).Since then, a-Si drew attentions of scientists. In addition,luminescence which can be only weakly observed in crystalline silicon(c-Si) can be observed at a high efficiency in a-Si and therefore, a-Sihas been researched for solar cells (for example, U.S. Pat. No.4,064,521).

However, a-Si developed for solar cells can not be directly used for thepurpose of photoconductive layers of practical electrophotographicimage-forming members.

Solar cells take out solar energy in a form of electric current andtherefore, the a-Si film should have a low dark resistance for thepurpose of obtaining efficiently the electric current at a good SN ratio[photo-current (Ip)/dark current (Id)], but if the resistance is so low,the photosensitivity is lowered and the SN ratio is degraded. Therefore,the dark resistance should be 10⁵ -10⁸ ohm.cm.

However, such degree of dark resistance is so low for photoconductivelayers of electrophotographic image-forming members that such a-Si filmcan not be used for the photoconductive layers.

Photoconductive materials for electrophotographic apparatuses shouldhave gamma value at a low light exposure region of nearly 1 since theincident light is a reflection light from the surface of materials to becopied and power of the light source built in electrophotographicapparatuses is usually limited.

Conventional a-Si can not satisfy the conditions necessary forelectrophotographic processes.

Another report concerning a-Si discloses that when the dark resistanceis increased, the photosensitivity is lowered. For example, an a-Si filmhaving dark resistance of about 10¹⁰ ohm.cm shows a loweredphotoconductive gain (photocurrent per incident photon). Therefore,conventional a-Si film can not be used for electrophotography even fromthis point of view.

Other various properties and conditions required for photoconductivelayers of electrophotographic image-forming member such as electrostaticcharacteristics, corona ion resistance, solvent resistance, lightfatigue resistance, humidity resistance, heat resistance, abrasionresistance, cleaning properties and the like have not been known as fora-Si films at all.

This invention has been accomplished in the light of the foregoing. Thepresent inventors have continued researches and investigations withgreat zeal concerning application of a-Si to electrophotographicimage-forming member. The invention is based on the discovery thatlamination of a hydrogenated amorphous silicon (hereinafter calleda-Si:H) layer and an organic compound layer described in the followingprovides an electrophotographic image-forming member which can be usedwith sufficient practicality and is extremely superior to theconventional image-forming member in almost all respects.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrophotographicimage-forming member, the preparing process for which is able to becarried out in an apparatus of a closed system to avoid the undesirableeffects to man and which electrophotographic image-forming member is notharmful to living things as well as man and further to environment uponthe use and therefore, causing no pollution.

Another object of the present invention is to provide anelectrophotographic image-forming member which has moisture resistance,thermal resistance and constantly stable electrophotographic propertiesand is of all environmental type.

A further object of the present invention is to provide anelectrophotographic image-forming member which has a high light fatigueresistance and a high corona discharging resistance, and is notdeteriorated upon repeating use.

Still another object of the present invention is to provide anelectrophotographic image-forming member which can give high qualityimages having a high image density, sharp half tone and high resolution.

A still further object of the present invention is to provide anelectrophotographic image-forming member which has a highphotosensitivity, a wide spectral sensitivity range covering almost allthe visible light range and fast photoresponse properties.

Still another object of the present invention is to provide anelectrophotographic image-forming member which has abrasion resistance,cleaning properties and solvent resistance.

A still further object of the present invention is to provide anelectrophotographic image-forming member which requires few restrictionswith respect to the period of time required until the commencement ofdevelopment of electrostatic image since formation of such image and theperiod of time required for the development.

According to an aspect of the present invention, there is provided animage-forming member for electrophotography which comprises a chargegeneration layer for generating movable carrier by excitation ofelectromagnetic wave, said charge generation layer being composed ofhydrogenated amorphous silicon, a charge transport layer into whichcarrier generated in said charge generation layer is injected and whichtransports the injected carrier, said charge transport layer beingcomposed of an organic compound, and a substrate for electrophotographyon which said charge generation layer and charge transport layer areoverlaid.

According to another aspect of the present invention there is providedan image-forming member for electrophotography which comprises asubstrate for electrophotography and a charge generation layer, saidcharge injection layer being sensitive to electromagnetic wave andhaving a depletion layer formed by junction of two layers composed oftwo types of hydrogenated amorphous silicons having different electricproperties, said depletion layer acting as a layer generating movablecarrier when said layer is subjected to action of electromagnetic wave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 are schematic cross-sectional views of preferred examples ofelectrophotographic image-forming members according to the presentinvention,

FIG. 7 is a schematic illustration of an apparatus which is used toprepare an electrophotographic image-forming member of the presentinvention in accordance with the sputtering method,

FIG. 8 is a schematic illustration of an apparatus which is used toprepare an electrophotographic image-forming member of the presentinvention in accordance with the capacitance type of glow dischargingmethod, and

FIG. 9 is a schematic illustration of an apparatus which is used toprepare an electrophotographic image-forming member of the presentinvention in accordance with the inductance type of glow dischargingmethod.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Representative examples of the electrophotographic image forming memberare shown in FIGS. 1-6.

An electrophotographic image forming member 101 in FIG. 1 contains asubstrate 102, a charge generation layer 103 capable of generatingmovable carriers by electromagnetic wave excitation, and a chargetransport layer 104 composed of an organic compound which the carriersgenerated in the layer 103 are efficiently injected into and whichtransports the carriers. Layer 104 has a free surface 105.

Charge generation layer 103 according to the present invention cangenerate movable carriers by action of electromagnetic wave whenirradiated by the electromagnetic wave as one step of a process forforming electrostatic images on image forming member 101.

According to the present invention, since charge generation layer 103should have a function as mentioned above, it is necessary that carriersenough to form electrostatic images having a substantially good contrastgenerate in charge generation layer 103. In other words, eithersubstrate 102 or layer 104 is preferably formed in such a way that theelectromagnetic wave sufficiently reaches charge generation layer 103.

For example, in FIG. 1, when an electromagnetic wave is projected fromthe side of layer 104, material and thickness of layer 104 are to beselected in such a manner that the electromagnetic wave passes throughlayer 104 and reaches layer 103 and the amount of the electromagneticwave is enough to generate a sufficient amount of carrier in layer 103.On the contrary, when an electromagnetic wave is projected from the sideof substrate 102, the substrate 102 is to be made taking the conditionsas mentioned above into consideration.

The order of layers of image forming member 101 in FIG. 1, that is,substrate 102, layer 103, and layer 104, may be changed. For example,substrate 102 is mounted on layer 104 and as the result, layer 103 has afree surface. In such layer structure, when an electromagnetic wave isprojected from the side of layer 103, it is not necessary to selectlayer 104 and substrate 102 by taking the above mentioned conditionsinto consideration. On the contrary, when an electromagnetic wave isprojected from the side of substrate 102, it is necessary to selectlayers 102 and 104 in such a manner that a sufficient amount of theelectromagnetic wave reaches layer 103 so as to form a sufficient amountof carrier.

Substrate 102 may be conductive or insulating. Examples of conductivesubstrates are metals such as Al, Cr, Mo, Au, Ir, Nb, Ta, V, Ti, Pt, Pdand the like, their alloys, stainless steels, and the like. Examples ofinsulating substrates are films or sheets of synthetic resins such aspolyesters, polyethylene, polycarbonates, cellulose triacetate,polypropylene, polyvinyl chloride, polyvinylidene chloride,polystyrenes, polyamides and the like, glass, ceramics, paper and thelike.

At least one surface of the insulating substrate is preferablyconductivized and another layer is mounted on said conductivizedsurface. For example, in case of glass, the surface is conductivizedwith In₂ O₃, SnO₂, or the like, and in case of a synthetic resin filmsuch as a polyester film, the surface is conductivized by vacuum vapordeposition, electron beam vapor deposition, sputtering or the like usingAl, Ag, Pb, Zn, Ni, Au, Cr, Mo, Ir, Nb, Ta, V, Ti, Pt or the like, or bylaminating with such metal.

The shape of substrate may be a type of drum, belt, plate or otheroptional shape. When a continuous high speed copying is desired, anendless belt or drum shape is desirable.

Thickness of the substrate may be optionally determined so as to producea desired electrophotographic image forming member. When theelectrophotographic image forming member is desired to be flexible, itis preferable that the substrate is as thin as possible. However, insuch a case the thickness is usually more than 10 microns from theviewpoints of manufacturing, handling and mechanical strength of thesubstrate.

The charge generation layer according to the present invention (e.g.layer 103 in FIG. 1) is composed of a hydrogenated amorphous silicon(hereinafter called a-Si:H) of the following type.

○1 n-type a-Si:H

Containing a donor only or containing both a donor and an acceptor wherethe content of donor (Nd) is higher.

○2 N⁺ -type a-Si:H

A type of ○1 which has a particularly strong n-type characteristic (Ndis much higher).

○3 p-type a-Si:H

Containing an acceptor only or containing both an acceptor and a donorwhere the content of acceptor (Na) is higher.

○4 p⁺ -type a-Si:H

A type of ○3 which has a particularly strong p-type characteristic (Nais much higher).

○5 i-type a-Si:H where Na≃Nd≃0 or Na≃Nd.

a-Si:H which constitutes, for example, layer 103 and satisfies theconditions as described below has the following excellentcharacteristics so that electrophotographic image forming membersproduced from the a-Si:H have various excellent electrophotographiccharacteristics.

Since the light absorption coefficient is as large as 10⁴ cm⁻¹ or morein the visible light region, it is possible to thin the chargegeneration region in the direction of thickness of the layer to beformed, generate charges in a high concentration and enhance the chargeinjection efficiency to a great extent.

The a-Si:H according to the present invention gives only a little amountof charge carrier formed by thermal excitation and therefore, the darkresistivity can be 10¹² ohm.cm or more and the dark decay is low as isclear from 0.5 m/sec. or more of the time constant. The light responsetime is as fast as 10 m/sec. or less. Therefore, according to thepresent invention, there can be obtained electrophotographic imageforming members of excellent electrophotographic characteristics andsuitable for a high speed copying.

Charge generation layer 103 may be produced on substrate 102 bydepositing a-Si:H on substrate 102 in a desired thickness by glowdischarge, sputtering, ion plating, ion implantation or the like.

These manufacturing methods may be optionally selected depending uponmanufacturing conditions, capital investment, manufacture scales,electrophotographic properties and the like. Glow discharge ispreferably used because controlling for obtaining desirableelectrophotographic properties is relatively easy and impurities ofGroup III or Group V of the Periodic Table can be introduced into thecharge generation layer composed of a-Si:H in a substitutional type forthe purpose of controlling the characteristics.

Further, according to the present invention, glow discharge andsputtering in combination can be conducted in the same system to formthe charge generation layer.

According to the present invention, the charge generation layer 103 iscomposed of hydrogenated a-Si for the purpose of enhancing darkresistivity and photosensitivity of the electrophotographic imageforming member.

A charge generation layer 103 composed of a-Si:H may be prepared byincorporating hydrogen in the layer upon forming the layer 103 accordingto the following method.

In the present invention, "H is contained in a layer" means one of, or acombination of the state, i.e. "H is bonded to Si", and "ionized H isweakly bonded to Si in the layer", and "present in the layer in a formof H₂ ".

In order to incorporate H in layer 103, a silicon compound such assilanes, for example, SiH₄, Si₂ H₆, and the like is introduced into adeposition system upon forming layer 103 and then heat-decomposed orsubjected to glow discharge to decompose the compound and incorporate Has layer 103 grows.

For example, when charge generation layer 103 is produced by a glowdischarge, a silicon hydride gas such as SiH₄, Si₂ H₆ and the like maybe used as the starting material for forming the a-Si and, therefore, His automatically incorporated in layer 103 upon formation of layer 103by decomposition of such silicon hydride.

Where reactive sputtering is employed, in a rare gas such as Ar or a gasmixture atmosphere containing a rare gas the sputtering is carried outwith Si as a target while introducing H₂ gas into the system orintroducing a silicon hydride gas such as SiH₄, Si₂ H₆ and the like orintroducing B₂ H₆, PH₃ or the like gas which can act as a source ofimpurities for doping layer 103.

The present inventors have found that an amount of H in layer 103composed of a-Si:H is a very important factor which determines whetherthe electrophotographic image forming member can be practically used.

Practically usable electrophotographic image forming members usuallycontain 1-40 atomic percent, preferably, 5-30 atomic percent of H in thecharge generation layer 103. When the content of H is outside of theabove range, the electrophotographic image forming member has a very lowor substantially no sensitivity to electromagnetic wave, and increase incarrier when irradiated by electromagnetic wave is a little and furtherthe dark resistivity is markedly low.

Controlling an amount of H to be contained in the charge generationlayer 103 can be effected by controlling the deposition substratetemperature and/or an amount of a starting material introduced into thesystem which is used for incorporating H.

In order to produce a charge generation layer 103 having a type selectedfrom ○1 - ○5 as mentioned as above, upon conducting glow discharge orreactive sputtering, the charge generation layer is doped with an n-typeimpurity (the charge generation layer is rendered a type ○1 or ○2 , ap-type impurity (the charge generation layer is rendered a type ○3 or ○4, or with both of them while the amount of impurity to be added iscontrolled. According to the present inventors' discovery, bycontrolling the concentration of impurities in a-Si to a range of 10¹⁵-10¹⁹ cm⁻³ there can be obtained a-Si:H having a property ranging from astronger n-type (or a stronger p-type) to a weaker n-type (or a weakerp-type).

As an impurity used for doping a-Si:H to make the a-Si:H p-type theremay be mentioned elements of Group III A of the Periodic Table such asB, Al, Ga, In, Tl and the like, and as an impurity for doping a-Si:H tomake the a-Si:H n-type, there may be mentioned elements of Group V A ofthe periodic Table such as N, P, As, Sb, Bi and the like.

These impurities are contained in the a-Si:H in an order of ppm. so thatproblem of pollution is not so serious as that for a main component of aphotoconductive layer. However, it is naturally preferable to payattention to such problem of pollution. From this viewpoint, B, As, Pand Sb are the most appropriate taking into consideration electrical andoptical characteristics of the charge generation layer to be produced.

An amount of impurity with which a-Si:H is doped may be appropriatelyselected depending upon electrical and optical characteristics of thecharge generation layer. In case of impurities of Group III A of theperiodic Table, the amount is usually 10⁻⁶ -10⁻³ atomic percent,preferably, 10⁻⁵ -10⁻⁴ atomic percent, and in case of impurities ofGroup V A of the Periodic Table, the amount is usually 10⁻⁸ -10⁻³ atomicpercent, preferably 10⁻⁸ -10⁻⁴ atomic %.

The a-Si:H may be doped with these impurities by various methodsdepending upon the type of method for preparing the a-Si:h. These willbe mentioned later in detail.

According to the present invention, in case of FIG. 1 and FIG. 2,thickness of the charge generation layer (e.g. 103) is usually more than0.1 micron so as to obtain a practically sufficient amount of chargeproduced by excitation with an electromagnetic wave.

On the other hand, the upper limit of the thickness is usually 10microns, preferably 7 microns from the viewpoint of shortening the timerequired for producing the charge generation layer composed of a-Si:Hand decreasing the manufacturing cost though the thickness usually usedin the field of electrophotography may be employed.

According to the present invention, the charge transport layer 104 is alayer into which carriers generated in the charge generation layer 103is efficiently injected and which effectively transports the carriersthus injected. Therefore, layer 104 is made of a material capable ofeffectively transporting the injected carriers and is mounted on layer103 in such a manner that layer 104 is electrically contacted with layer103 so as to facilitate the injection of carriers from layer 103.

Materials for layer 104 capable of satisfying such conditions are, forexample, organic compounds since many organic compounds havefilm-shapeability, adhesivity and the required electric resistance.

Among the organic compounds, organic photoconductive materials can bepreferably used.

Representative organic photoconductive materials for the chargetransport layer 104 are:

carbazoles such as polyvinylcarbazole (PVK), carbazole,N-ethylcarbazole, N-isopropylcarbazole, N-phenylcarbazole and the like;

pyrenes such as pyrene, tetraphenylpyrene, 1-methylpyrene, azapyrene,1-ethylpyrene, 1,2-benzpyrene, 3,4-benzpyrene, 4,5-benzpyrene,acetylpyrene, 1,4-bromopyrene, polyvinylpyrene and the like;

anthracene, tetracene, tetraphene, perylene, phenanthrene,2-phenylnaphthalene, and the like;

chrysenes such as chrysene, 2,3-benzochrysene, picene, benzo[b]chrysene,benzo[c]chrysene, benzo[g]chrysene and the like;

phenylindole and the like;

aromatic heterocyclic polyvinyl compounds such as polyvinyltetracene,polyvinylperylene, polyvinylpyrene, polyvinyltetraphene and the like;

polyacrylonitrile and the like;

fluorene, fluorenone and the like;

polyazophenylene and the like;

pyrazoline derivatives such as 2-pyrazoline, pyrazoline hydrochloride,pyrazoline picrate, N-p-tolylpyrazoline and the like;

polyimidazopyrrolone, polyimidimidazopyrrolone, and the like;

polyimide, polyimidoxazole, polyamidobezimidazole, poly-p-phenylene andthe like;

erythrosine and the like;

2,4,7-trinitro-9-fluorenone (TNF), PVK:TNF, 2,4,5,7-tetranitrofluorenoneand the like; and

dinitroanthracene, dinitroacridine, tetracyanophyrene,dinitroanthraquinone and the like.

In FIG. 1, a layer having a function similar to that of layer 104 may beadditionally formed between layer 103 and substrate 102.

Thickness of the charge transport layer 104 may be optionally selecteddepending upon the requested properties of layer 104 and a relation withlayer 103. It is usually 5-80 microns, preferably 10-50 microns.

It is preferred to dispose a barrier layer capable of preventinginjection of carriers from the substrate 102 side uponelectroconductivizing for forming electrostatic images between substrate102 and a layer disposed on said substrate in case of an image formingmember where charge transport layer 104 or charge generation layer 103has a free surface and the free surface is electroconductivized forforming electrostatic images.

Materials for such barrier layer may be optionally selected dependingupon the type of substrate 102 and electric properties of a layerdisposed on substrate 102.

Representative materials for the barrier are MgF₂, Al₂ O₃, SiO, SiO₂ andthe like insulating inorganic compounds, polyethylene, polycarbonates,polyurethanes, poly-para-xylylene and the like insulating organiccompounds, and Au, Ir, Pt, Rh, Pd, Mo and the like metals.

In FIG. 2, electrophotographic image forming layer 201 is composed of acovering layer 205 having a free surface 206, a charge generation layer204 composed of a-Si:H, a charge transport layer 203 composed of anorganic compound and a substrate 202, and is substantially the same asthe image forming member 101 in FIG. 1 except that the covering layer iscontained. However the properties required for the covering layer 205are different from one another depending upon the electrophotographicprocess employed. For example, when an electrophotographic process ofU.S. Pat. Nos. 3,666,364 or 3,734,609 is employed, the covering layer205 is insulating and electrostatic charge retentivity whenelectroconductivized is sufficiently high and thickness of the layer isthicker than a certain value. On the contrary, in case of anelectrophotographic process such as Carlson process, thickness of thecovering layer 205 is required to be very thin since it is desired thatelectric potential at the light portion is very small. Covering layer205 is disposed taking into consideration the required electricproperties, and further covering layer 205 should not adversely affectchemically or physically the charge generation layer 204 and the chargetransport layer 203 which the covering layer is contacted with, andadditionally, covering layer 205 is formed taking an electrical contactproperty and an adhesivity with respect to a layer which the coveringlayer contacts, and humidity resistance, abrasion resistance, cleaningproperty and the like.

Thickness of covering layer 205 is optionally determined depending uponthe required properties and the type of material used. It is usually0.5-70 microns.

When covering layer 205 is required to have a protective function, thethickness is usually less than 10 microns while when it is required tobehave as an electrically insulating layer, the thickness is usuallymore than 10 microns.

However, these values of thickness for a protective layer and for aninsulating layer are only examples and may vary depending upon type ofthe material, type of the electrophotographic process employed andstructure of the electrophotographic image forming member, and thereforethe thickness, 10 microns, is not always a critical value.

Referring to FIG. 3, electrophotographic image forming member 301comprises a substrate 302, a charge generation layer 303, and a chargetransport layer 304. Charge generation layer 303 contains a depletionlayer 306, and layer 304 has a free surface 305.

The image forming member 301 in FIG. 3 is substantially the same as themember 101 in FIG. 1 except that structure of the charge generationlayer 303 is different from that of layer 103. The depletion layer 306produces movable carriers when irradiated by an electromagnetic wave ata step of electromagnetic wave irradiation in a process of formingelectrostatic images on the image forming member 301.

One of substrate 302 and layer 304 should be formed in such a mannerthat carriers sufficient to form electrostatic images having asubstantially sufficient contrast are produced in the depletion layer306 depending upon the direction in which the electromagnetic wave isprojected to the image forming member 301, that is, the electromagneticwave sufficiently reaches the depletion layer 306. In this point, thesituation is similar to FIG. 1.

The order of disposing layers 302, 303 and 304 does not limit thepresent invention, but the order may be changed, for example, layer 302may overlie layer 304 and layer 303 has a free surface. In case of thelatter order of layer arrengement, when electromagnetic wave isprojected from the side of layer 303, it is not necessary to payparticular attention to layer 304 and substrate 302 with respect toreaching of electromagnetic wave to depletion 306. On the contrary, whenelectromagnetic wave is projected from the side of substrate 302,materials for substrate 302 and layer 304 and thickness of each layershould be selected in such a manner that electromagnetic wave reachesdepletion layer 306 so as to generate sufficient carriers at depletionlayer 306.

The depletion layer 306 may be formed in layer 303 by selecting at leasttwo kinds of a-Si:H of ○1 - ○5 types and forming layer 303 in such a waythat two different kinds of materials are brought into junction. Inother words depletion layer 306 may be formed as a junction portionbetween an i-type a-Si:H layer and a p-type a-Si:H layer by forming ani-type a-Si:H layer on substrate 302 having desired surfacecharacteristics and forming a p-type a-Si:H layer on said i-type layer.

Hereinafter, an a-Si:H layer on a substrate 302 side with respect to adepletion layer 306 is called an inner layer while that on a freesurface 305 side is called an outer layer. In other words, a depletionlayer 306 is formed at a transition region in the junction between aninner a-Si:H layer and an outer a-Si:H layer when a charge generationlayer 303 is produced in such a way that two different types of a-Si:Hlayers.

At a normal state, the depletion layer 306 is in a state that freecarriers are depleted and therefore it shows a behavior of so-calledintrinsic semiconductor.

In the present invention, an inner layer 307 and an outer layer 308which are constituting a charge generation layer 303 are composed of thesame a-Si:H and the junction portion (depletion layer 306) is ahomojunction and therefore, inner layer 307 and outer layer 308 form agood electrical and optical junction and the energy bands of the innerlayer and the outer layer are smoothly joined. Further, in depletionlayer 306 there exists an intrinsic electric field (diffusion potential)(inclination of energy band) when depletion layer 306 is formed. Thus, acarrier forming efficiency is enhansed and in addition, recombinationprobability of the formed carrier is decreased, that is, the quantumefficiency is increased and light response becomes fast and formation ofresidual charge is prevented.

In view of the foregoing, carriers produced in depletion layer 306 byirradiation of an electromagnetic wave such as light advantageously workeffectively to form electrostatic images.

The image forming member according to the present invention iselectroconductivized on the free surface in such a manner that thecharge polarity capable of applying a voltage of reverse bias todepletion layer 306 when electrostatic images are formed. When thisreverse bias is applied to the depletion layer, thickness of depletionlayer 306 increases at a rate of about 1/2 power of the voltage appliedto depletion layer 306. For example, at a high voltage (higher than 10⁴V/cm), thickness of depletion layer 306 is several or several tens timesthat when it is not electroconductivized. Further, application ofreverse bias to depletion layer 306 makes the intrinsic electric field(diffusion potential) formed by the junction steep. This renders theabove mentioned effect more remarkable.

According to the present invention, as mentioned previously, the innerlayer 307 and the outer layer 308 are composed of the same material, andthe depletion layer 306 is formed by junction between inner layer 307and outer layer 308 and therefore, the whole charge generation layer 303can be advantageously formed by a continuous manufacturing process.

Thickness of depletion layer 306 can be determined by difference ofFermi level before joining inner layer 307 and outer layer 308 to bejoined and dielectric constants of these layers, that is concentrationof impurities doping the layer so as to control the a-Si:H layer to bejoined to the type of ○1 - ○5 above. In particular, by controllingdoping amount of the impurities the thickness can be changed to severaltens Å to several microns.

As mentioned above, when reverse bias is applied, thickness of thedepletion layer 306 can be increased so that it can be increased up toseveral hundred Å to several tens microns. Therefore, thickness ofdepletion layer 306 varies depending upon the degree of reverse bias.

However, when a reverse bias of a high electric field is applied todepletion layer 306, it is necessary to determine the concentration ofimpurities and voltage to be applied as mentioned below in such a mannerthat neither tunneling nor avalanche breakdown is caused. In otherwords, when the concentration of impurities is so high, even arelatively low reverse bias causes tunneling and avalanche breakdown andtherefore, a sufficient broadening of the depletion layer 306 (decreasein electric capacity) and a sufficient electric field to the depletionlayer 306 can not be obtained.

According to the present invention, depletion layer 306 plays a role ofabsorbing electromagnetic wave to produce carriers and therefore, it isdesirable to use a thick layer so as to absorb the electromagnetic waveincident on depletion layer 306 as far as possible. However, on theother hand, the intensity of intrinsic electric field formed indepletion layer 306 per unit thickness, an important factor which lowersrecombination probability of carriers formed in depletion layer 306, isinversely proportional to thickness of the layer. Therefore, as far asthis point is concerned, a thinner depletion layer 306 is preferable.

In view of the foregoing, in case of an image forming member 301 in FIG.3, the following two points should be considered so as to attainsufficiently the purpose. That is, according to the present invention,formation of carriers by irradiation of electromagnetic wave is mostlyeffected in depletion layer 306 so that it is necessary to form eitherinner layer 307 or outer layer 308 depending upon the direction ofirradiation of electromagnetic wave to an image forming member 301 insuch a manner that carriers sufficient to form electrostatic imageshaving a sufficient contrast are produced in depletion layer 306, thatis the irradiated electromagnetic wave sufficiently reaches thedepletion layer.

In case of usual electrophotographic image forming members, visiblelight is used as the electromagnetic wave. Therefore, it is necessaryfor the purpose of attaining the above purpose to form one of innerlayer 307 and outer layer 308 as a layer at the electromagnetic waveirradiating side in such a manner that at least one part of thedepletion layer 306 is present within a distance of 5000Å from thesurface of the electromagnetic wave irradiation side of the chargegeneration layer 303 when electroconductivized since the lightabsorption coefficient of a-Si:H ranges from 5×10⁵ to 10⁴ cm⁻¹ at awavelength range of 400-700 nm.

In addition, with respect to the lower limit of thickness of one ofinner layer 307 and outer layer 308 at electromagnetic wave irradiationside, since it is necessary only that a depletion layer 306 is formed byjunction between inner layer 307 and outer layer 308, the thinner thecharge generation layer, the higher the carrier generation efficiency indepletion layer 306 with respect to an irradiation amount ofelectromagnetic wave. Therefore, a thin charge generation layer ispreferable as far as the manufacturing technique is available.

When an a-Si:H layer is rendered p-type (including p⁺ -type) or n-type(including n⁺ -type), the dark resistance varies to a great extentdepending upon the concentration of impurities, and most of the layercan not be used for electrophotography since the dark resistance is toolow.

This reason is that when the resistance is so low, the surfaceresistance is not enough to prevent electric charge from escaping to atraverse direction upon forming electrostatic images and therefore,highly sensitive latent images can not be obtained and there is not adifference in amount between thermal excited free carrier and lightexcited free carrier and thereby electrostatic latent images can not beformed.

However, in the present invention, even in case of anelectrophotographic image forming member having a charge generationlayer formed as free surface, there is a broadening of thickness of adepletion layer caused by application of a reverse bias to the depletionlayer. This fact means that free carriers are ejected and this resultsin that even when resistance of the outer layer is relatively low, theouter layer behaves as a high resistance in appearance.

Further, charging in a direction to a reverse bias ejects free carriersin the outer layer to a direction of the surface and thereby causes asimilar change in the outer layer.

Consequently, as a material for constituting the outer layer, there canbe used a material which gives a broadening effect of a depletion effectand an ejection effect of free carriers as explained above as far as thedegrees of these effects are enough to attain the purpose of the presentinvention even if the material is of a relatively low electricresistance and therefore, has been thought unusable.

A layer which is not at the electromagnetic wave irradiation side, i.e.one of inner layer 307 and outer layer 308, (a layer which is at a sideopposite to the electromagnetic wave irradiation side with respect todepletion layer 306), can be formed in such a manner that it functionsto transport effectively charges generated in the depletion layer 306and, in addition, can contribute to electric capacity of chargegeneration layer 303.

In view of the foregoing, such layer is formed usually in the thicknessof 0.1-10 microns, preferably, 0.1-7 microns taking into considerationeconomy including manufacturing cost and manufacturing time of the imageforming member.

In FIG. 3, there is shown a preferred embodiment of an image formingmember of the present invention, that is, an inner layer 307 and anouter layer 308 are two different types of a-Si:H layers selected from○1 - ○5 types and joined to form a charge generation layer 303 and itssuperiority to prior art is explained. The above mentioned selection ismade, for example, a combination of p-type and i-type, of p⁺ -type andi-type, of n⁺ -type and i-type, or p-type and n-type.

Furthermore, a charge generation layer composed of junction of threedifferent types of a-Si:H layers selected from ○1 - ○5 types is also apreferred embodiment of the present invention. The combination of p·i·nor n·i·p from the side of substrate 302. In this case, there are twodepletion layers in a charge generation layer.

In this case, it is possible to apply a large electric field since ahigh electric field can be applied to the divided two depletion layersand thereby it becomes easy to obtain a high surface potential.

When a charge generation layer has a layer-structure of p·i·n or n·i·pfrom the substrate side, the following feature exists and variouselectrophotographic processes can be applied. Injection of charge into acharge generation layer from the substrate side can be prevented.Further, since it is possible to irradiate electromagnetic wave fromboth the surface side and the substrate side, irradiating both sides bythe same image or a simultaneous add on system by irradiation ofdifferent images are possible. And further, it is possible to irradiatefrom the back side for eliminating electrostatic images (irradiationfrom the substrate side) or irradiate from the back side by the latermentioned NP system (accelerating a charge injection from the substrateside) or irradiate from the back side so as to enhance the durability.

Referring to FIG. 4, an electrophotographic image forming member 401 hasa covering layer 405 having a free surface 406, a substrate 402, acharge transport layer 403, and a charge generation layer 404 composedof an inner layer 408 and an outer layer 409 and a depletion layer 407in said layer.

The member 401 is substantially the same as the image forming member 1in FIG. 3 except the covering layer.

In the image forming member having a depletion layer in the chargegeneration layer as illustrated in FIGS. 3 and 4, the concentration ofimpuriries doping a-Si:H layers of ○1 - ○5 which can form inner layerand outer layer may be as mentioned previously. It is preferable forforming a particularly effective depletion layer to select Na and Nd insuch a manner that the value of NaNd/(Na+Nd) in the charge generationlayer is within the following range.

When a particular reverse bias voltage is applied to a depletion layer,the upper limit of NaNd/CNa is determined in such a manner that neithertunneling nor avalanche breakdown occurs. It is usually, for example,about 10¹⁸ cm⁻³. As the lower limit, it is usually the number of freedangling bond of Si per unit volume in the charge generation layer, N,and it is preferably more than N by 1/2 place or more, particularlypreferably one place or more.

Other embodiments of the present invention are shown in FIG. 5 and FIG.6.

Referring to FIG. 5, an electrophotographic image forming member 501 issubstantially the same as the image forming member 301 in FIG. 3 exceptthat there is not a charge transport layer.

The member 501 consists of a substrate 502 and a charge generation layer503 composed of a-Si:H. The layer 503 has a free surface 504 on whichimages are formed and the layer 503 contains a depletion layer 505.

Inner layer 506 and outer layer 507 are composed of a-Si:H selected from○1 - ○5 types as explained in FIG. 3 concerning an image forming member301.

Referring to FIG. 6, an image forming member 601 is substantially thesame as the image forming member 501 in points of layer-structure andlayer forming materials except that a covering layer 607 similar to acovering layer 405 in FIG. 4 on a charge generation layer 603, that is,the member 601 consists of a substrate 602, a charge generation layer603 in which an inner layer 605 and an outer layer 606 are joined toform a depletion layer 604, and the above mentioned covering layer 607.

The charge generation layer of electrophotographic image forming membersaccording to the present invention may be prepared by glow discharge andsputtering.

Referring to FIG. 7, an apparatus for producing a charge generationlayer by sputtering is shown.

A deposition chamber 701 contains a substrate 702 which is fixed to aconductive fixing member 703 electrically isolated from depositionchamber 701. A charge generating layer is formed on the substrate 702.

Below substrate 702 is disposed heater 704 for heating substrate 702. Atthe upper portion there is disposed a polycrystal or single crystalsilicon target 705 on an electrode for sputtering in a position facingsubstrate 702.

Between fixing member 703 to which substrate 702 is fixed and silicontarget 705, a high frequency voltage is applied by a high frequencypower source 734. Gas pressure vessels 707, 708, 709 and 710 areconnected with deposition chamber 702 through inflow valves 711, 712,713 and 714, flow meters 715, 716, 717 and 718, outflow valves 719, 720,721 and 722, respectively, and auxiliary valve 723. A desired gas can beintroduced into deposition chamber 701 from gas pressure vessels 707,708, 709 and 710.

Gas pressure vessel 707 contains H₂ which can be introduced intodeposition chamber 701 so as to deposit a-Si:H on substrate 702 bysputtering of silicon target 705.

Gas pressure vessel 708 contains an atmosphere gas to be introduced intodeposition chamber 701 for effecting sputtering.

Gas pressure vessels 709 and 710 are gas materials for introducingimpurities into a-Si:H layer so as to control said layer to a type of○1 - ○5 , for example, PH₃, P₂ H₄, B₂ H₆, AsH₃ and the like arecontained.

By using the apparatus of FIG. 2, there can be formed an a-Si:H layer onsubstrate 702. Main valve 724 is fully opened to evacuate depositionchamber 701 by exhausting air to the direction of arrow B, and thenauxiliary valve 723, inflow valves 711-714 and out flow valves 719-722to bring the pressure in deposition chamber 701 to a predetermineddegree of vacuum.

Then, heater 704 is turned on to heat substrate 702 to a particulartemperature. When an a-Si:H layer is formed by a sputtering method, thetemperature of substrate 702 is usually 50°-350° C., preferably,100°-200° C. This substrate temperature affects a growing speed of thelayer, structure of the layer and presence or absence of voids, anddetermines partly physical properties of the layer thus formed.Therefore, substrate temperature should be sufficiently controlled. Thesubstrate temperature may be kept at a constant temperature duringforming the a-Si:H layer or may be raised or lowered or raised andlowered accordingly as the a-Si:H layer grows. For example, at theinitial stage of formation of an a-Si:H layer the substrate temperatureis kept at a relatively low temperature T₁ and when the a-Si:H layergrows to a certain extent, formation of a-Si:H layer is conducted insuch a manner that the substrate temperature is raised from T₁ to atemperature T₂ which is higher than T₁ and at the final stage offormation of the a-Si:H layer the substrate temperature is lowered fromT₂ to a temperature T₃ which is lower than T₂ to form the a-Si:H layer.In this way, it is possible to obtain an a-Si:H layer in whichelectrical and optical properties of the formed a-Si:H layer areconstant or vary continuously in the thickness direction of the layer.

Since the layer growing speed of a-Si:H is slower than that of othermaterials such as Se and the like, as the layer thickness becomes thick,the a-Si:H (that near the substrate side) formed at the initial stage isconsidered to change its properties at the initial stage during theformation procedure. Therefore, in order to obtain an a-Si:H layerhaving uniform characteristics in the direction of thickness of layer,it is desirable to raise the substrate temperature from the beginning tothe end of the layer formation.

This substrate temperature control procedure also can be employed incase of a glow discharge method.

After confirming that substrate 702 is heated to a predeterminedtemperature, inflow valves 711-714, outflow valves 719-722 and auxiliaryvalve 723 are closed.

While watching an outlet pressure gauge 731, valve 68 is graduallyopened to control the outlet pressure of gas pressure vessel 708 to apredetermined pressure and then inflow valve 712 is fully opened to flowan atmosphere gas such as Ar gas into flow meter 716, and further,auxiliary valve 723 is opened and then while adjusting main valve 724and outflow valve 720, the atmosphere gas is introduced into depositionchamber 701 and the chamber 701 is kept at a predetermined degree ofvacuum.

Then, while watching outlet gauge 730, valve 726 is gradually opened tocontrol the outlet pressure of gas pressure vessel 707. Then, inflowvalve 711 is fully opened to let H₂ gas flow into flow meter 715, andwhile controlling main valve 724 and outflow valve 719, H₂ gas isintroduced into deposition chamber 701 to maintain a predeterminedvacuum. Introduction of H₂ gas into deposition chamber 701 is omittedwhen it is not necessary to incorporate H in an a-Si:H layer formed onsubstrate 702.

A flow rate of an atmosphere gas such as H₂, Ar and the like intodeposition chamber is determined in such a manner that an a-Si:H layerof desired properties. For example, when an atmosphere gas and H₂ gasare mixed, a pressure of the gas mixture in deposition chamber 701 isusually 10⁻³ -10⁻¹ Torr, preferably 5×10⁻³ -3×10⁻² Torr. Ar gas may bereplaced by a rare gas such as He.

When it is not necessarily required to dope an a-Si:H layer with animpurity, after introducing an atmosphere gas and H₂, or an atmospheregas into deposition chamber 701 until the pressure becomes apredetermined degree of vacuum, a high frequency voltage is appliedbetween a fixing member 703 to which substrate 702 is fixed and anelectrode for sputtering by using a high frequency power source 734 at apredetermined frequency and a voltage and discharged and the formed ionsof the atmosphere gas such as Ar ion sputter a silicon target to form ana-Si:H layer on substrate 702.

When impurities are introduced into an a-Si:H layer formed, a rawmaterial gas for forming impurities is introduced into depositionchamber 701 from gas pressure vessel 709 or 710 upon forming an a-Si:Hlayer.

In case of the image forming member having the layer structure shown inFIG. 1 and FIG. 2, the charge generation layer is formed in a way asmentioned above.

In case of the image forming member having a depletion layer in a chargegeneration layer as shown in FIG. 3 through FIG. 6, a charge generationlayer is formed in a way as shown below.

As mentioned above, an inner layer is formed on substrate 702 in apredetermined thickness and then an outer layer is formed to completethe whole layer of a charge generation layer in a manner as shown below.

As an example, in case of forming an inner layer by introducing only H₂gas from gas pressure vessel 707 and an atmosphere gas from gas pressurevessel 708 into deposition chamber 701, an outer layer of a typedifferent from a type of the inner layer is produced by introducing H₂gas, an atmosphere gas and a raw material gas for impurities from gaspressure vessel 709 or 710 into deposition chamber 701.

As another example, in case of forming an inner layer by introducing,for example, a mixture of H₂ gas, an atmosphere gas and a raw materialgas for impurities into deposition chamber 701, an outer layer having atype different from that of the inner layer is formed by introducing amixture of H₂ gas and an atmosphere gas, or a mixture of H₂ gas, anatmosphere gas and a raw material gas for impurities from gas pressurevessel 710 into deposition chamber 701.

As a further example, in case of forming an inner layer by introducingH₂ gas, an atmosphere gas and a raw material gas for impurities from gaspressure vessel 709 into deposition chamber 701, an outer layer isformed by introducing the same gases as used above except that theamount of introduction of a raw material gas for impurities intodeposition chamber 701 per unit time is different from that in the aboveprocedure.

By forming an inner layer and an outer layer, there is formed adepletion layer at a junction portion between the inner layer and theouter layer and thereby a charge generation layer of theelectrophotographic image forming member according to the presentinvention.

When a charge generation layer having two depletion layers such as alayer structure of p.i.n, a layer structure of p⁺ ·p·n, a layerstructure of n·p·i and the like is desired, the charge generation layercan be produced by appropriately selecting the above mentioned threemethods.

With respect to FIG. 7, there is explained a sputtering method by highfrequency electric field discharging, but a sputtering method by adirect current electric field discharging may be also used.

According to the sputtering method by applying a high frequency voltage,the frequency is usually 0.2-30 MHz, preferably 5-20 MHz and thedischarge current density is usually 0.1-10 mA/cm², preferably 0.1-5mA/cm², more preferably 1-5 mA/cm². For obtaining a sufficient power,there is employed usually a voltage of 100-5000 V, preferably 300-5000V.

When a sputtering method is used, a growing speed of an a-Si:H layer ismainly determined by substrate temperature and discharging conditionsand is a factor affecting physical properties of the formed layer. Thegrowing speed of an a-Si:H layer for attaining the purpose of thepresent invention is usually 0.5-100 Å/sec., preferably 1-50 Å/sec.

In a way similar to a glow discharging method, an a-Si:H layer formed bydoping with impurities can be also adjusted to n-type or p-typeaccording to a sputtering method.

A method of introducing impurities is the same in both a sputteringmethod and a glow discharging method. For example, PH₃, P₂ H₄, B₂ H₆ orthe like compound in a gaseous state is introduced into depositionchamber 701 upon forming an a-Si:H layer and the a-Si:H layer is dopedwith P or B as an impurity. An impurity may be incorporated in a formeda-Si:H layer by ion implantation.

FIG. 8 shows a glow discharge deposition apparatus for producing ana-Si:H layer by a capacitance type glow discharging method.

A glow-discharge deposition chamber 801 contains a substrate 802 forforming an a-Si:H layer thereon and fixed on a fixing member 803. Belowsubstrate 802 there is a heater 804 for heating substrate 802. At theupper portion of deposition chamber 801 there is wound a capacitancetype electrode 806-1, 806-2 connected with a high frequency power source805. When the power source 805 is turned on, a high frequency is appliedto the electrodes 806-1, 806-2 to cause a glow discharge in depositionchamber 801. The upper portion of deposition chamber 801 is connectedwith a gas introducing conduit through which a gas from gas pressurevessel 807, 808 or 809 is introduced into deposition chamber 801. Flowmeters 810, 811 and 812 are used for detecting a flow rate of a gas, andflow rate controlling valves 813, 814 and 815, valves 816, 817, and 818,and an auxiliary valve 819 are provided.

The lower portion of deposition chamber 801 is connected with anexhausting apparatus (not shown) through a main valve 820. Valve 821 isused for breaking vacuum in deposition chamber 801.

By using a glow discharging deposition apparatus in FIG. 8, an a-Si:Hlayer having desired properties can be produced on substrate 802 asshown below.

A substrate 802 subjected to a particular cleaning treatment is fixed toa fixing member 803 with the cleaned surface kept upward, or a substrate802 having a charge transport layer composed of an organic compound isfixed to fixing member 803.

Surface of substrate 802 may be cleaned as shown below. It can becleaned with an alkali or acid, (a kind of chemical treatment), or bydisposing a substrate cleaned to some extent in deposition chamber 801at a fixed portion and then applying glow discharge. In the latter case,cleaning substrate 802 and formation of an a-Si:H layer can be carriedout in the same system without breaking vacuum and thereby it can beavoided that dirty matters and impurities attach to the cleaned surface.After fixing substrate 802 to fixing member 803, main valve 820 is fullyopened to evacuate deposition chamber 801 to bring the pressure down toabout 10⁻⁵ Torr. Then heater 804 starts to heat substrate 802 up to apredetermined temperature, and the temperature is kept. Then, auxiliaryvalve 819 is fully opened, and then valve 816 of gas pressure vessel 807and valve 817 of gas pressure vessel 808 are fully opened. Gas pressurevessel 807 is, for example, for a diluting gas such as Ar and gaspressure vessel 808 is for a gas forming a-Si:H, for example, siliconhydride gas such as SiH₄, Si₂ H₆, Si₄ H₁₀ or their mixture. Pressurevessel 809 may be used, if desired for storing a gas capable ofincorporating impurities in an a-Si:H layer, for example, PH 3, P₂ H₄,B₂ H₆ and the like. Flow rate controlling valves 813 and 814 aregradually opened while obseving flow meters 810 and 811 to introduce adiluent gas, e.g., Ar, and a gas for forming a-Si:H, e.g., SiH₄ intodeposition chamber 801. The diluting gas is not always necessary, butonly SiH₄ may be introduced into the system. When Ar gas is mixed with agas for forming a-Si:H, e.g. SiH₄, and then introduced, the amount ratiomay be determined depending upon each particular situation. Usually thegas for forming a-Si:H is more than 10 vol. % based on the diluting gas.As the diluting gas, a rare gas such as He may be used in place of Ar.When gases are introduced from pressure vessels 807 and 808 intodeposition chamber 801, main valve 820 is adjusted to keep a particularvacuum degree, usually, an a-Si:H layer forming gas of 10⁻¹² -3 Torr.Then, to electrodes 806-1 and 806-2 is applied a high frequency voltage,for example, 0.2-30 MHz, from high frequency power source 805 to causeglow discharge in deposition chamber 801, and SiH₄ is decomposed todeposit a-Si:H on substrate 802 to form an a-Si:H layer.

Impurities may be introduced into an a-Si:H layer to be formed byintroducing a gas from pressure vessel 809 into deposition chamber 801upon forming an a-Si:H photoconductive layer. By controlling valve 815,an amount of gas introduced into deposition chamber 801 from pressurevessel 809 can be controlled. Therefore, an amount of impuritiesincorporated in an a-Si:H layer can be optionally controlled and inaddition, the amount may be varied in the direction of thickness of thea-Si:H layer.

In FIG. 8, the glow discharge deposition apparatus uses a glow dischargeprocess of RF (radio frequency) capacitance type, but in place of saidtype process, there may be used a glow discharge process of RFinductance type or DC diode type. Electrodes for glow discharge may bedisposed in or outside of deposition chamber 801.

In order to efficiently carry out glow discharge in a glow dischargeapparatus of capacitance type as shown in FIG. 8, current density isusually 0.1-10 mA/cm², preferably 0.1-5 mA/cm², more preferably, 1-5mA/cm², and further the voltage is usually 100-5000 V, preferably300-5000 V, so as to obtain a sufficient power.

Characteristics of an a-Si:H layer depend on a temperature of substrateto a great extent and therefore, it is preferable to control thetemperature strictly. The temperature of substrate according to thepresent invention is usually 50°-350° C., preferably 100°-200° C. so asto obtain an a-Si:H layer for electrophotography having desirablecharacteristics. In addition, the substrate temperature may be changedcontinuously or batchwise to produce desirable characteristics.

FIG. 9 illustrates diagrammatically a glow discharge depositionapparatus for producing a charge generation layer by inductance typeglow discharge.

Glow discharge deposition chamber 901 contains substrate 902 on which ana-Si:H layer is formed. Substrate 902 is fixed to fixing member 903.Under substrate 902 is disposed heater 904 to heat substrate 902.Inductance coil 906 connected to a high frequency power source 905 iswound around the upper portion of deposition chamber 901. When the powersource 905 is on, high frequency wave is applied to the coil 906 tocause glow discharge in deposition chamber 901. To the top of depositionchamber 901 is connected a gas introducing pipe capable of introducinggases in gas pressure vessels 907, 908 and 909 when required. The gasintroducing pipe is equipped with flow meters 910, 911 and 912, inflowvalves 913, 914 and 915, outflow valves 916, 917 and 918 and auxiliaryvalve 919.

The bottom portion of deposition chamber 901 is connected to anexhausting device (not shown) through main valve 920. Valve 928 is usedfor breaking vacuum in deposition chamber 901.

An a-Si:H layer having a desired characteristics is formed on substrate902 by using the glow discharge deposition apparatus in FIG. 9.

Cleaned substrate 902 is fixed to fixing member 903 with the cleanedsurface upward. After fixing a substrate 902 to a fixing member 903,deposition chamber 901 is evacuated to the direction shown by arrow A byfully opening a main valve 920 and thereby the pressure in system isbrought down to about 10⁻⁵ Torr.

Then, auxiliary valve 919 is fully opened, and outflow valves 916, 917and 918, and inflow valves 913, 914 and 915 are fully opened, andfurther flow meters 910, 911 and 912 are evacuated. Then, auxiliaryvalve 919, inflow valves 913, 914 and 915, and outflow valves 916, 917and 918 are closed after deposition chamber 901 reaches a predetermineddegree of vacuum, and heater 904 is turned on to heat substrate 902 to apredetermined temperature and then the temperature is kept. Gas pressurevessel 907 contains a gas for forming a-Si:H such as SiH₄, Si₂ H₆, Si₄H₁₀ and mixtures thereof. Gas pressure vessels 908 and 909 containsgases for doping an a-Si:H layer with impurities so as to control thea-Si:H layer to a type of ○1 - ○5 . The gases are, for example, PH₃, P₂H₄, B₂ H₆, AsH₃ and the like.

After confirming that substrate 902 reaches a predetermined temperature,valve 921 of gas pressure vessel 907 is opened, and pressure of outletpressure gauge is adjusted to a predetermined pressure, and then inflowvalve 913 is gradually opened to flow a gas for forming a-Si:H such asSiH₄ and the like into flow meter 910. Auxiliary valve 919 is opened toa predetermined position, and while watching Pirani gauge 929, outflowvalve 916 is gradually opened to adjust a flow rate of a gas fed todeposition chamber 901 from gas pressure vessel 907. Where it is notnecessary to dope the formed a-Si:H layer with the impurities, mainvalve 920 is controlled watching Pirani gauge 927 at a time ofintroducing a gas for forming a-Si:H into deposition chamber 901 fromgas pressure vessel 907 to obtain a predetermined degree of vacuumusually 10⁻² -3 Torr as a gas pressure upon forming the a-Si:H layer.

Then a high frequency power having a predetermined high frequency(usually 0.2-10 MHz) is supplied to an induction coil 906 wound arounddeposition chamber 901 from a high frequency power source 905 to causeglow discharge in deposition chamber 901 and thereby a gas for forminga-Si:H and as SiH₄ is decomposed to form an a-Si:H layer on substrate902.

If impurities are to be introduced into the a-Si:H layer, a gas forforming impurities is introduced into deposition chamber 901 from gaspressure vessel 908 or 909 upon forming the a-Si:H layer.

A charge generation layer of an image forming member as shown in FIGS. 1and 2 may be produced as mentioned above.

Image forming members having a depletion layer in a charge generationlayer as shown in FIG. 3 through FIG. 6 may be produced by the followingmethods.

As mentioned above, an inner layer is formed on substrate 902 in apredetermined thickness and then an outer layer is formed to completethe whole layer of a charge generation layer in a manner as shown below.

As an example, in case of forming an inner layer by introducing only agas for forming a-Si:H from gas pressure vessel 907 into depositionchamber 901, an outer layer of a type different from a type of the innerlayer is produced by introducing a gas for forming a-Si:H from vessel907 and a raw material gas for impurities from gas pressure vessel 908or 909 into deposition chamber 901.

As another example, in case of forming an inner layer by introducing,for example, a gas for forming a-Si:H from gas pressure vessel 907 and araw material gas for impurities from vessel 908 into deposition chamber901, an outer layer having a type different from that of the inner layeris formed by introducing a gas for forming a-Si:H from gas pressurevessel 907, or a mixture of a gas for forming a-Si:H and a raw materialgas for impurities from gas pressure vessel 909 into deposition chamber901.

As a further example, in case of forming an inner layer by introducing amixture of a gas for forming a-Si:H from vessel 907 and, for example, araw material gas for impurities from gas pressure vessel 908 intodeposition vessel 901, an outer layer is formed by introducing a mixtureas mentioned above except that the amount ratio of the gas for forminga-Si:H and a gas for impurities is different from that used in theabove.

By forming an inner layer and an outer layer, there is formed adepletion layer at a junction portion between the inner layer and theouter layer. When a charge generation layer having two depletion layerssuch as a layer structure of p·i·n, a layer structure of p·n·i, a layerstructure of n·i·p and the like is desired, the charge generation layercan be produced by appropriately selecting the above mentioned threemethods.

In the apparatus of FIG. 9, characteristics of an a-Si:H layer depend ona temperature of substrate to a great extent and therefore, it ispreferable to control the temperature strictly. The temperature ofsubstrate is usually 50°-350° C., preferably 100°-200° C. so as toobtain an a-Si:H layer for electrophotography having desirablecharacteristics. In addition, the substrate temperature may be changedcontinuously or batchwise to produce desirable characteristics. Growingspeed of the a-Si:H layer also affects physical properties of theresulting a-Si:H layer to a great extent, and according to the presentinvention, it is usually 0.5-100 Å/sec., preferably 1-50 Å/sec.

Other procedure conditions mentioned in case of FIG. 8 may be used forthe apparatus of FIG. 9.

The invention will be understood more readily by reference to thefollowing examples; however, these examples are intended to illustratethe invention and are not to be construed to limit the scope of theinvention.

EXAMPLE 1

In accordance with the procedure described below, an electrophotographicimage-forming member of the present invention was prepared by using anapparatus as shown in FIG. 8, and image forming treatment was applied tothe image-forming member.

An aluminum substrate was cleaned in such a manner that the surface ofthe substrate was treated with a 1% solution of NaOH and sufficientlywashed with water and then dried. This substrate, which was 1 mm inthickness and 10 cm×5 cm in size, was firmly disposed at a fixedposition in a fixing member 803 placed at a predetermined position in adeposition chamber 801 for glow discharge so that the substrate was keptapart from a heater 804 equipped to the fixing member 803 by about 1.0cm.

The air in the deposition chamber 801 was evacuated by opening fully amain valve 820 to bring the chamber to a vacuum degree of about 5×10⁻⁵Torr. The heater 804 was then ignited to heat uniformly the aluminumsubstrate to 150° C., and the substrate was kept at this temperature. Asubsidiary valve 819 was fully opened, and subsequently a valve 816 of abomb 807 to which Ar was charged and a valve 817 of a bomb 808 which wasfilled with SiH₄ were also opened fully, and thereafter, flow amountcontrolling valves 813, 814 were gradually opened so that Ar gas andSiH₄ gas were introduced into the deposition chamber 801 from the bombs807, 808. At that time, the vacuum degree in the deposition chamber 801was brought to and kept at about 0.075 Torr. by regulating the mainvalve 820.

A high frequency power source 805 was switched on to apply a highfrequency voltage of 13.56 MHz between electrodes 806-1 and 806-2 sothat a glow discharge was caused, thereby depositing and forming ana-Si:H layer on the aluminum substrate. At that time, the glow dischargewas initiated with an electric power of 5 W. Further, the growth rate ofthe a-Si:H layer was about 4 angstroms per second and the vacuumdeposition was effected for about 20 minutes and further the thus formeda-Si:H layer had a thickness of 0.5 microns.

After completion of the deposition, while the main valve 820, valves 816and 817, flow amount controlling valves 813 and 814, and subsidiaryvalve 819 were closed, a leak valve 821 was opened to break the vacuumstate in the deposition chamber 801. The formed structure was taken outfrom the apparatus.

On the thus formed a-Si:H layer was coated a coating liquid which hadbeen prepared by dissolving a mixture of TNF and PVK (1:1 in ratio byweight) in a mixed liquid of toluene and cyclohexane (1:1 in ratio byvolume), in accordance with the doctor blade method. This structure wasallowed to stand in atmosphere at 80° C. for about two hours toevaporate the toluene and cyclohexane. The formed TNF:PVK layer had athickness of about 20 microns after drying. The image-forming treatmentwas applied to the thus prepared image-forming member in the followingmanner.

Positive corona discharge was applied to the surface of theimage-forming member with a power source voltage of 6,000 V in a darkplace. The imagewise exposure was then conducted in an exposure quantityof 15 lux.sec. to form an electrostatic image, which was then developedwith a negatively charge toner in accordance with the cascade method.The developed image was transferred to a transfer paper and fixed. Atthis time, an extremely sharp transferred image with a high resolutionwas obtained although the period of time required until completion ofthe developing step since the charging step was only several seconds.Further, even when the treatment period of time exceeded 10 seconds, thecontrast of the transferred image was hardly decreased.

EXAMPLE 2

An a-Si:H layer of 0.5 micron in thickness was formed on an aluminumsubstrate in the same manner as in Example 1. Onto the a-Si:H layer wasapplied a coating liquid prepared by dissolving a mixture of TNF andpolyethyleneterephthalate (hereinafter called "PET") (0.4:1 in ratio byweight) in a liquid mixture of toluene and cyclohexane, in accordancewith the doctor blade method. This structure was allowed to stand inatmosphere at 80° C. for about two hours to evaporate the solvent in theapplied coating liquid. The TNF:PET layer was of about 20 micronsthickness after drying.

The thus prepared image-forming member was subjected to the positivecorona charging with a voltage of 6,000 V in a dark place and the imageexposure was conducted in an exposure quantity of 15 lux.sec. from theimage forming surface so that an electrostatic image was formed. Theelectrostatic image was then developed with a negatively charged tonerin the cascade manner. The developed image was transferred to a transferpaper and finally fixed. The obtained image was extremely sharp with ahigh resolution.

EXAMPLE 3

In Example 1, an a-Si:H layer having a thickness of 0.5 microns wasformed on the aluminum substrate in the same manner as in Example 1except that the glow discharge was carried out while the SiH₄ gas wasmixed with B₂ H₆ gas in a ratio of 0.01%. On the a-Si:H layer was coateda coating liquid which had been prepared by dissolving a mixture oftetracene and polycarbonate resin (1:10 by weight ratio) in toluene, inaccordance with the doctor blade method. It was allowed to stand inatmosphere at 80° C. for about two hours to evaporate the solvent. Thelayer of tetracene and polycarbonate resin had a thickness of about 20microns after drying.

The thus prepared image-forming member was subjected to negative coronadischarge with a voltage of 5,500 V in a dark place and the imageexposure was effected in an exposure quantity of 15 lux sec. from theside of the image-forming surface of the member to form an electrostaticimage, which was then developed with a positively charged toner in thecascade method. The developed image was transferred to a transfer paperand fixed to obtain an image with an extremely good sharpness and highresolution.

EXAMPLE 4

An aluminum substrate having a thickness of 1 mm and a size of 10 cm×50cm was cleaned in such a manner that the surface of the substrate wastreated with a 1% solution of NaOH and sufficiently washed with waterand then dried. On the surface of the substrate was coated coatingliquid which had been obtained by dissolving unpolymerizedimidazopyrrolone powder in a mixed liquid of dimethylacetamide andN-methyl-2-pyrrolidone, in the doctor blade method. This structure wasallowed to stand in atmosphere at about 80° C. for about one hour toevaporate the dimethylacetamide and N-methyl-2-pyrrolidone, and furtherto stand in atmosphere at about 300° C. for about three hours for thepurpose of heat treatment. The polyimidazopyrrolone layer formed on thealuminum substrate was 20 microns in thickness after drying.

Further, an a-Si:H layer was formed on the polyimidazopyrrolone layer inaccordance with the following sputtering method using an apparatus shownin FIG. 7.

The substrate 702 having the polyimidazopyrrolone layer was firmlydisposed at a predetermined position of fixing member 703 positioned ina deposition chamber 701 so that the polyimidazopyrrolone layer might befaced upwards and kept apart from a heater 704 by 1.0 cm or so. Further,a target 705 of polycrystalline silicon having a purity of 99.999% wasfixed over the substrate 702 so that it might be kept apart from thesubstrate 702 by about 8.5 cm. A main valve 724, subsidiary valve 723,outflow valves 719 and 720 were each opened to evacuate the air in thedeposition chamber 701 and in flow meters 715 and 716 so that the vacuumdegree was brought to about 1×10⁻⁶ Torr. Thereafter, the valves 723, 719and 720 were closed. The heater 704 was ignited to heat uniformly thesubstrate 702 to about 150° C. and the substrate was kept at thattemperature.

A valve 723 was fully opened, and subsequently a valve 726 of a bomb 707was also fully opened. Thereafter, an inflow valve 711 and outflow valve719 were gradually opened to introduce H₂ gas into the depositionchamber 701 from the bomb 707 while the vacuum degree in the depositionchamber 701 was brought to 5.5×10⁻⁴ Torr by regulating the main valve724 with the flow meter 715 being carefully observed. Successively,after fully opening a valve 727 of a bomb 708, an inflow valve 712 andoutflow valve 720 were gradually opened with a flow meter 716 beingcarefully observed, to introduce Ar gas into the deposition chamber 701in which the vacuum degree was adjusted to 5×10⁻³ Torr.

A high frequency power source 734 was switched on to apply a highfrequency voltage of 13.56 MHz and 1 KV between the substrate 702 andpolycrystalline silicone target 705 so that a discharge was caused,thereby, starting formation of an a-Si:H layer on thepolyimidazopyrrolone layer. This operation was conducted continuouslywith the growth rate of the a-Si:H layer being controlled to about twoangstroms per second for 40 minutes. The formed a-Si:H layer was about0.5 micron in thickness.

The thus prepared image-forming member was used to effect imageformation process in the same manner as in Example 2. As a result, agood transferred image with a high quality was obtained.

EXAMPLE 5

In the same manner as in Example 4, a polyimidazopyrrolone layer havinga thickness of 15 microns and an a-Si:H layer having a thickness of 0.5microns were formed on the aluminum substrate. Further, thereon wasformed a TNF:PET layer having a thickness of 15 microns in the sameprocedure as in Example 2.

Image forming process was conducted by using the image-forming memberthus obtained in the same manner as in Example 2. As a result, atransferred image of high quality was obtained.

EXAMPLE 6

An image-forming member was prepared according to the same procedure asin Example 1 except that as the substrate was used a sheet ofpolyethyleneterephthalate having a thickness of 100 microns on which analuminum thin layer was formed by the vapor deposition. The thusobtained member was employed to conduct the image forming process in thesame manner as in Example 1 except that the image exposure was carriedout from the side of the substrate of the image-forming member. Thetransferred image as thus obtained was formed to be of high quality.

EXAMPLE 7

In the same procedure as in Example 4, a polyimidazopyrrolone layer of15 microns thick was formed on the aluminum substrate and an a-Si:Hlayer of 0.5 micron thick was overlaid on the polyimidazopyrrolonelayer. Thereafter, polycarbonate resin was coated onto the a-Si:H layerto form a transparent insulating layer having a thickness of 15 micronsafter drying.

To the insulating layer surface of the thus prepared image-formingmember was applied negative corona discharge with a charging voltage of5,500 V as the primary charging simultaneously with the whole surfaceexposure being uniformly effected from the side of the insulating layer.Since then, after passage of 5 seconds or so, positive corona dischargewas conducted with a voltage of 6,000 V as the secondary chargingsimultaneously with the image exposure being conducted in an exposurequantity of 20 lux.sec., and the whole surface of the image-formingmember was then exposed uniformly to form an electrostatic image. Thisimage was developed with a positively charged toner according to thecascade method, transferred to a transfer paper and fixed so that asharp image with a high resolution was obtained.

EXAMPLE 8

In Example 1, an a-Si:H layer having a thickness of 0.5 microns wasformed on the aluminum substrate in the same manner as in Example 1except that the glow discharge was carried out while the SiH₄ gas wasmixed with B₂ H₆ gas in a ratio of 0.01%. On the a-Si:H layer was coateda coating liquid which had been obtained by dissolvingpoly-N-vinylcarbazole in toluene, in accordance with the doctor blademethod. It was allowed to stand in atmosphere at 80° C. for about twohours to evaporate the solvent. The poly-N-vinylcarbazole layer had athickness of about 20 microns after drying.

The thus prepared image-forming member was subjected to negative coronadischarge with a voltage of 5,500 V in a dark place and the imageexposure was effected in an exposure quantity of 15 lux.sec. from theside of the image-forming surface to form an electrostatic image, whichwas then developed with a positively charged toner in the cascademethod. The developed image was transferred to a transfer paper andfixed to obtain an image with an extremely good sharpness and highresolution.

EXAMPLE 9

An image-forming member was prepared by using an apparatus as shown inFIG. 9 placed in a sealed clean room in accordance with the followingprocedure.

A molybdenum substrate 902 having a thickness of 0.2 mm and a diameterof 5 cmφ, the surface of which had been cleaned, was securely disposedin a fixing member 903 placed in a deposition chamber 901 for glowdischarge. The substrate 902 was heated with accuracy of ±0.5° C. bymeans of a heater 904 disposed in the fixing member 903. At that time,the temperature of the substrate was measured in such a manner that theback side of the substrate was brought into direct contact with achromel-alumel thermocouple.

The closed state of all valves in the apparatus was confirmed. A mainvalve 920 was fully opened to evacuate the air in the deposition chamber901 so that the vacuum degree in the chamber was brought to about 5×10⁻⁶Torr. The input voltage of the heater 904 was increased and changedwhile the temperature of the molybdenum substrate was observed so thatthe substrate might be kept at 150° C.

Subsequently, a subsidiary 919 and outflow valves 916, 917 and 918 werefully opened to evacuate sufficiently the air in flow meters 910, 911,912. As a result, those meters were brought to vaccum state. The valves916, 917, 918 and 919 were closed. Thereafter, a valve 921 of a bomb 907to which silane gas of 99.999% purity had been charged and a valve 922of a bomb 908 which had been filled with diborane gas were opened sothat the pressure in outlet pressure gauges 924, 925 was adjusted to 1kg/cm². Inflow valves 913 and 914 were gradually opened to introduce thesilane gas and diborane gas into the flow meters 910 and 911,respectively. Successively, the subsidiary valve 919 was graduallyopened, and further the outflow valves 916 and 917 were also graduallyopened. At this time, the flow amount of the silane gas and diborane gaswas adjusted so that the reading of the flow meter 911 might be 0.08%based on the reading of the flow meter 910. While the reading of aPirani gauge 927 was carefully observed, the subsidiary valve 919 wasregulated to bring the deposition chamber 901 to a vacuum degree of1×10⁻² Torr. After the inside pressure of the chamber 901 became stable,the main valve 920 was gradually closed so that the reading of thePirani gauge might become 0.075 Torr.

After confirming that the inside pressure of the chamber 901 wasstabilized, a high frequency power source 905 was switched on in orderto input a high frequency power of 5 MHz to an induction coil 906 sothat a glow discharge was initiated with an input power of 30 W in theinside of the portion winded with the coil 906 (that is, the upper areaof the chamber). The same condition was continued and kept for one hour.Since then, the high frequency power source 905 was switched off to stopthe glow discharge (formation of an inner layer). The valve 922 of thebomb 908 and the outflow valve 917 were closed.

Successively, the high frequency power source 905 was again switched onin order to give rise to a glow discharge in the chamber 901. The glowdischarge was further continued for one hour. Thereafter, the heater 904as well as the high frequency power source 905 was turned off (formationof an outer layer).

After the substrate temperature reached 100° C., the outflow valve 916and subsidiary valve 919 were closed, while the main valve 920 was fullyopened to bring the inside of the chamber 901 to 10⁻⁵ Torr or below.Thereafter, the main valve 920 was closed, and the inside of the chamber901 was brought to atmospheric pressure by way of a leak valve 928, andthen the substrate 902 was taken out from the apparatus. As the resultof the above operation, an a-Si:H layer (charge generation layer) wasformed on the substrate 902 and such layer had a total thickness ofabout two microns.

Next, a TNF:PVK layer of about 20 microns in thickness was furtherformed on the above a-Si:H layer in accordance with the same procedureand condition as in Example 1.

The thus prepared image-forming member was subjected to the imageforming process given below. First, positive corona discharge wasapplied with a power source voltage of 6,000 V to the surface of themember on which an image was formed, in a dark place. The image exposurewas conducted in an exposure quantity of 15 lux.sec. from the side ofthe image forming surface to an electrostatic image, which was thendeveloped with a negatively charged toner according to the cascademethod. The developed image was transferred to a transfer paper andfixed. At that time, although the treatment period of time requireduntil the completion of the developing step since the charging step wasonly several seconds, a sharp transferred image with a high resolutionwas obtained. Further, even when the treatment period of time exceeded10 seconds, lowering of the contrast of the transferred image was hardlyobserved.

EXAMPLE 10

An a-Si:H layer having a thickness of two microns was formed on amolybdenum substrate by using the same procedure and condition as inExample 9.

Further, a TNF:PET layer having a thickness of about 20 microns wasformed on the a-Si:H layer in accordance with the same procedure andcondition as in Example 2.

The thus obtained image-forming member was subjected to the followingimage forming process. Positive corona discharge was applied with apower source voltage of 6,000 V to the image-forming member in a darkplace. Next, the image exposure was effected in an exposure quantity of15 lux.sec. from the surface on which images are formed, to form anelectrostatic image, which was then developed with a negatively chargedtoner according to the cascade method. The developed image wastransferred to a transfer paper and fixed. As a result, an extremelysharp image with high resolution was obtained.

EXAMPLE 11

An a-Si:H layer (charge generatation layer) of two microns in thicknesshaving therein a depletion layer was formed on a molybdenum substrateaccording to the same procedure as in Example 9 except that the formingorder of the outer and inner layers was inverted. Further, atetracene:polycarbonate resin layer of about 20 microns in thickness wasformed on the a-Si:H layer in accordance with the same procedure andcondition as in Example 3 to obtain an image-forming member.

To the image-forming member was applied negative corona discharge with apower source voltage of 5,500 V in a dark place. Image exposure wasconducted in an exposure quantity of 15 lux.sec. from the surface of themember on which images were to be formed, to form an electrostaticimage, image, which was then developed with a positively charged toner.The developed image was transferred to a transfer paper followed byfixation. As a result, a sharp image with high resolution was obtained.

EXAMPLE 12

An aluminum substrate having a thickness of 1 mm and a size of 10 cm×5cm was cleaned in such a manner that the surface of the substrate wastreated with a 1% solution of NaOH and sufficiently washed with waterand then dried. A polyimidazopyrrolone layer having a thickness of about20 microns was formed on the surface of the substrate by using the sameprocedure and condition as in Example 4. Further, an a-Si:H layer(charge generation layer) was formed on the polyimidazopyrrolone layerin accordance with the following sputtering method by means of anapparatus shown in FIG. 7.

The substrate 702 having the polyimidazopyrrolone layer was securelyfixed to a fixing member 703 disposed in a predetermined position of adeposition chamber 701 so that the polyimidazopyrrolone layer might befaced upward and the substrate 702 was kept apart from a heater 704 by1.0 cm or so. A polycrystalline silicon (purity 99.999%) target 705 wasfixed onto an electrode opposed to the substrate 702 so that it might beopposed and made parallel to the substrate and further kept apart fromthe substrate by about 4.5 cm.

The air in the depositon chamber 701 was evacuated by fully opening amain valve 724 to bring the chamber to a vacuum degree of 5×10⁻⁷ Torr.At that time, all valves of the apparatus except for the main valve 724were closed. A subsidiary valve 723 and outflow valves 719, 720, 721,722 were opened to evacuate sufficiently the air. Thereafter, theoutflow valves 719, 720, 721, 722 and subsidiary valve 723 were closed.

The substrate 702 was kept at 200° C. by means of the heater 704. Avalve 726 of a bomb 707 which had been filled up with hydrogen gas(purity 99.99995%) was opened to adjust the outlet pressure to 1 kg/cm²while an outlet pressure gauge 730 was observed. Subsequently, an inflowvalve 711 was gradually opened to allow the hydrogen gas to flow into aflow meter 715, and successively the outflow valve 719 was graduallyopened and further the subsidiary valve 723 was also opened. While theinside pressure of the chamber 701 was measured by means of a pressuregauge 723, the outflow valve 719 was regulated to introduce the hydrogengas into the deposition chamber 701 so that the inside pressure of thechamber 701 might reach up to 5×10⁻⁵ Torr.

A valve 727 of a bomb 708 to which argon gas (purity: 99,9999%) had beencharged was opened and regulated so that the reading of an outletpressure gauge 731 might indicate 1 kg/cm². Thereafter, an inflow valve712 was opened and further the outflow 720 was gradually opened to allowthe argon gas to flow into the chamber 701. The outflow valve 720 wasgradually opened until the pressure gauge 725 indicated 5×10⁻⁴ Torr, andunder that condition, the flow amount of the argon gas was stabilized.Thereafter, the main valve 724 was gradually closed to bring the insidepressure of the chamber 701 to 1×10⁻² Torr.

Successively, a valve 728 of a bomb 709 containing therein diborane gas(purity: 99,9995%) was opened to adjust the reading of an outletpressure gauge 732 to 1 kg,/cm². An inflow valve 713 was opened and theoutflow valve 721 was gradually opened. At that time, the outflow valve721 was regulated while the reading of a flow meter 717 was observed, inorder to control the flow amount of the diborane gas so that such flowamount might be about 1.0% based on the flow amount of the hydrogen gasindicated by the flow meter 715.

After the flow meters 715, 716 and 717 became stabilized, a highfrequency power source 734 was switched on in order to input analternating power of 13.56 MH_(z), 1.6. KV between the target 705 andfixing member 703. Under this condition, stable discharging wascontinued for 40 minutes to form an inner layer.

Thereafter, the high frequency power source 734 was turned off todiscontinue the discharging. Successively, the outflow valves 719, 720and 721 were closed, while the main valve 724 was fully opened toevacuate the gas present in the chamber 701 so that vacuum degree in thechamber was brought up to 5×10⁻⁷ Torr.

Subsequently, similarly to the case of the inner layer formation, thehydrogen gas and argon gas were introduced into the deposition chamber701 and the opening degree of the main valve 724 was regulated to bringthe inside pressure of the chamber 701 to 2×10⁻² Torr. A valve 729 of abomb 710 containing therein phosphine gas (purity: 99,9995%) was openedto regulate the outlet pressure so that the reading of an outletpressure gauge 733 might indicate 1 kg/cm². An inflow valve 714 andoutflow valve 722 were gradually opened while a flow meter 718 wasobserved, in order to adjust the flow amount of the phosphine gas to1.0% based on that of the hydrogen gas. After the flow amount of thehydrogen, argon and phosphine gases became stable, the high frequencypower sourcc 734 was switched on to apply a voltage of 1.6 KV therebyconducting the discharge. Under that condition, the discharge wascontinued for 40 minutes. Thereafter, the power source 734 and heater704 were turned off. When the substrate temperature was decreased to100° C. or below, the outflow valves 719, 720 and 722 were closed andthe subsidiary valve 723 was also closed, while the main valve 724 wasfully opened to evacuate the gas in the chamber 701. Thereafter, themain valve 724 was closed, whereas a leak valve 735 was opened to bringthe chamber to atmospheric pressure. The substrate was taken out fromthe apparatus. The formed a-Si:H layer (charge generation layer) had athickness of two microns.

To the thus obtained image-forming member was applied positive coronacharging with a power source voltage of 6,000 V in a dark place. Theimage exposure was effected from the side of the surface of the memberon which an image was to be formed. in an exposure quantity of 15lux.sec. to form an electrostatic image, which was then developed with anegatively charged toner in accordance with the cascade method. Thedeveloped image was transferred to a transfer paper and fixed. As aresult, a clear image with high resolution was obtained.

EXAMPLE 13

In the same manner as in Example 12, a polyimidazopyrrolone layer ofabout 15 microns thick and a-Si:H layer (charge generation layer) of onemicron thick were formed on the aluminum substrate. Further, in the samemanner as in Example 2, a TNF:PET layer of about 15 microns thick wasformed.

The image forming process was conducted by using the thus preparedimage-forming member in the same procedure as in Example 12. As aresult, a transferred image of high quality was obtained.

EXAMPLE 14

An image-forming member was prepared according to the same procedure asin Example 9 except that as the substrate was used a sheet ofpolyethyleneterephthalate having a thickness of 100 microns on which analuminum thin layer was formed by the vapor deposition. The thusobtained member was employed to conduct the image-forming process in thesame manner as in Example 9 except that the image exposure was carriedout from the side of the substrate of the image-forming member. Thetransferred image as thus obtained was found to be of high quality.

EXAMPLE 15

In the same procedure as in Example 12, a polyimidazopyrrolone layer ofabout 15 microns thick was formed on an aluminum substrate and an a-Si:Hlayer (charge generation layer) of about one micron thick was overlaidon the polyimidazopyrrolone layer. Thereafter, polycarbonate resin wascoated onto the a-Si:H layer to form a transparent insulating layerhaving a thickness of 15 microns after drying.

To the insulating layer surface of the thus prepared image-formingmember was applied negative corona discharge with a charging voltage of5,000 V as the primary charging simultaneously with the whole surfaceexposure being uniformly effected from the side of the insulating layersurface. Since then, after passage of 5 seconds on so, positive coronadischarge was conducted with a charging voltage of 6,000 V as thesecondary charging simultaneously with the image exposure beingconducted in an exposure quantity of 20 lux.sec., and the whole surfaceof the image-forming member was then exposed uniformly to form anelectrostatic image. This image was developed with a positively chargedtoner according to the cascade method, transferred to a transfer paperand fixed so that a sharp image with a high resolution was obtained.

EXAMPLE 16

ITO (In₂ O₃ :S_(n) O₂ =20:1 shaped, burned at 600° C.) layer having athickness of 1200 angstroms was formed on one side surface of a glasssubstrate (trade name:Corning 7059, supplied by Dow Corning Co.) havinga thickness of 1 mm and a size of 4×4 cm, the both sides of which hadbeen polished, in accordance with the electron beam vapor depositionprocedure. The obtained structure was heated in atmosphere of oxygen at500° C.

The structure was disposed in the fixing member 903 in the apparatusshown in FIG. 9 similar to that used in Example 9 so that the ITO layermight be faced upward. Subsequently, in accordance with the sameprocedure as in Example 9, the inside of the deposition chamber 901 forglow discharge was adjusted to a vacuum degree of 5×10⁻⁶ Torr and thesubstrate temperature was kept at 170° C., and thereafter the silane gasin the bomb 907 was allowed to flow into the chamber 901 so that theinside of the chamber 901 was brought to 0.8 Torr. A valve 923 of a bomb909 containing therein phosphine was was opened to adjust the reading ofthe outlet pressure gauge 926 to 1 kg/cm². The inflow valve 915 wasopened and the outflow valve 918 was regulated while the flow meter 912was observed in order to control the flow amount of the phosphine gas sothat it might be 0.1% based on the flow amount of the silane gas fromthe bomb 907. Under such condition, the phosphine gas was mixed with thesilane gas from the bomb 907 and allowed to flow into the depositionchamber 901.

After the gas inflow become stable and the inside pressure of thechamber 901 was maintained at the constant level and further thesubstrate temperature was kept at 170° C., the high frequency powersource 905 was switched on to give rise to a glow discharge in a similarmanner to that in Example 9. This glow discharge was continued for 30minutes, and thereafter the high frequency power source 905 was turnedoff to discontinue the glow discharge, thereby completing the formationof an inner layer. The outflow valves 916 and 918 were closed, while thesubsidiary valve 919 and main valve 920 were fully opened to bring theinside of the chamber 901 to a vacuum degree of 5×10⁻⁶ Torr. Thesubsidiary valve 919 and main valve 920 were then closed. Next, theoutflow valve 916 was gradually opened and the subsidiary valve 919 andmain valve 920 were regulated to adjust the flow amount of the silanegas to the same flow amount as in case of forming the inner layer. Thepower source 905 was switched on to cause a glow discharge, which wascontinued for one hour. Thereafter, the heater 904 and power source 905were turned off. After the substrate temperature was decreased to 100°C., the outflow valve 916 was closed, while the main valve andsubsidiary valve 919 were fully opened to bring the inside of thechamber 901 to 10⁻⁵ Torr or below. The subsidiary valve 919 and mainvalve 920 were then closed and the inside of the chamber 901 was broughtto atmospheric pressure by means of the leak valve 928. The substratewas taken out which had an a-Si:H layer of about 3.5 microns in totalthickness.

A TNF:PVK layer having a thickness of 30 microns was formed on thea-Si:H layer in the same manner as in Example 1. The thus obtainedimage-forming member was tested with respect to the image formation. Themember was subjected to the image forming process comprising positivecorona charging with a voltage of 6 KV, image exposure conducted fromthe glass substrate side and development with a negatively chargeddeveloper. As a result, a good image was obtained with sufficientpracticality.

EXAMPLE 17

An image-forming member was prepared by using an apparatus as shown inFIG. 9 placed in a sealed clean room in accordance with the followingprocedure.

A molybdenum substrate 902 having a thickness of 0.2 mm and a diameterof 5 cmΦ, the surface of which had been cleaned, was securely disposedin a fixing member 903 placed in a deposition chamber 901 for glowdischarge. The substrate 902 was heated with accuracy of ±0.5° C. bymeans of a heater 904 disposed in the fixing member 903. At that time,the temperature of the substrate was measured in such a manner that theback side of the substrate was brought into direct contact with achromel-alumel thermocouple.

The closed state of all valves in the apparatus was confirmed. A mainvalve 920 was fully opened to evacuate the air in the deposition chamber901 so that the vacuum degree in the chamber was brought to about 5×10⁻⁶Torr. The input voltage of the heater 904 was increased and changedwhile the temperature of the molybdenum substrate was observed so thatthe substrate was kept at 150° C.

Subsequently, a subsidiary valve 919 and outflow valves 916, 917 and 918were fully opened to evacuate sufficiently the air in flow meters 910,911 and 912. As a result, the insides of those meters were brought tovacuum state. The valves 916, 917, 918, 913, 914 and 915 were closed.Thereafter, a valve 921 of a bomb 907 to which silane gas of 99.999%purity had been charged was opened so that the pressure in an outletpressure gauge 924 was adjusted to 1 kg/cm². An inflow valve 913 wasgradually opened to introduce the silane gas into the flow meter 910.Successively, the outlet valve 916 was gradually opened and thesubsidiary valve 919 was gradually opened. At that time, the subsidiaryvalve 919 was regulated with the reading of a Pirani gauge 927 beingcarefully observed, in order to bring the inside of the chamber 901 to1×10⁻² Torr. After the inside pressure of the chamber 901 became stable,the main valve 920 was gradually closed so that the reading of thePirani gauge might become 0.5 Torr.

After confirming that the inside pressure of the chamber 901 wasstabilized, a high frequency power source 905 was switched on in orderto input a high frequency power of 5 MHz to an induction coil 906 sothat a glow discharge was initiated with an input power of 30 W in theinside of chamber. Under the same condition, an a-Si:H layer (innerlayer) was allowed to grow on the substrate and such condition wascontinued for 5 hours. The power source 905 was turned off todiscontinue the glow discharge. A valve 922 of a bomb 908 containingtherein diborane gas (purity: 99.999%) was opened to adjust the pressureat an outlet pressure gauge 925 to 1 kg/cm², and an inflow valve 914 wasgradually opened to cause the diborane gas to flow in a flow meter 911.Thereafter, an outlet valve 917 was gradually opened and regulated sothat the reading of the flow meter 911 might indicate 0.08% of the flowamount of the diborane gas based on that of the silane gas from the bomb907.

Successively, the high frequency power source 905 was again switched onin order to give rise to a glow discharge in the chamber 901. The glowdischarge was further continued for one hour. Thereafter, the heater 904as well as the high frequency power source 905 was turned off (formationof an outer layer).

After the substrate temperature reached 100° C., the outflow valves 916,917 and subsidiary valve 919 were closed, while the main valve 920 wasfully opened to bring the inside of the chamber 901 to 10⁻⁵ Torr orbelow. Thereafter, the main valve 920 was closed, and the inside of thechamber 901 was brought to atmospheric pressure by way of a leak valve928, and then the substrate 902 was taken out from the apparatus. As theresult of the above operation, the formed a-Si:H layer had a totalthickness of about 6 microns.

The thus prepared image forming member was subjected to theimage-forming process. Corona charging with ⊖6 KV was applied to theimage-forming member for 0.2 sec. Immediately thereafter, the imageexposure was effected. At that time, the image-forming member wasexposed to light from a xenon lamp, from which light having a wavelengthrange of 550 nm or below was excluded by using a filter (trade name:V-058, supplied by Toshiba Kasei Kogyo K.K.), in an exposure quantity of15 lux.sec. through a transmission type test chart. Immediatelythereafter, the development was conducted with a positively chargeddeveloper (containing toner and carrier) to obtain a good toner image onthe surface of the image-forming member. The toner image was thentransferred onto a transfer paper while corona charging of ⊕5 KV wasapplied. As a result, a clear image of high density was obtained whichwas further excellent in the resolution, gradation and reproducibility.

On the other hand, corona charging with ⊕6 KV was applied to theimage-forming member, and the image exposure was effected in accordancewith the same procedure and condition as those in the foregoing.Further, the development was conducted with a negatively chargeddeveloper. The obtained image was found to be poor in the image densityand unclear as compared with the image obtained in the foregoing.

Further, the image-forming process first mentioned in this example wasrepeated except that three color filters, i.e., blue, green and redfilters were used in place of the filter V-058, respectively. In eithercase, substantially the same, excellent image was obtained on thetransfer paper.

EXAMPLE 18

In accordance with the following operation, an image-forming member wasprepared by using an apparatus shown in FIG. 7.

A platinum thin film having a thickness of about 800 angstroms wasdeposited onto a stainless steel plate having a thickness of 0.2 mm anda size of 10×10 cm, the surface of which had been cleaned, in accordancewith the electron beam vacuum-deposition. The thus treated stainlesssteel plate was used as a substrate 702.

The substrate 702 was fixed in a fixing member 703 enclosing a heater704 and a thermocouple in a deposition chamber 701. A polycrystallinesilicon (purity: 99.999%) target 705 was securely placed on an electrodeopposed to the substrate 702 so that it might be opposed to and madeparallel to the substrate 702 and further kept apart from the substrateby about 4.5 cm.

A main valve 724 was fully opened to evacuate the air in the inside ofthe chamber 701 to bring the chamber to a vacuum degree of 5×10⁻⁷ Torror so. At that time, other valves than the main valve 724 were allclosed. A subsidiary valve 723 and outflow valves 719, 720, 721 and 722were opened to evacuate sufficiently the air, and then the outflowvalves 719, 720, 721, 722 and subsidiary valve 723 were closed.

The substrate 702 was heated by heater 704 and kept at 200° C. A valve726 of a bomb 707 containing therein hydrogen gas (purity: 99.99995%)was opened to adjust the outlet pressure to 1 kg/cm² while an outletpressure gauge 730 was observed. Subsequently an inflow valve 711 wasgradually opened to allow the hydrogen gas to flow into a flow meter715, and successively the outflow valve 719 was gradually opened andfurther the subsidiary valve 723 also opened.

While the inside pressure of the chamber 701 was measured by a pressuregauge 725, the outflow valve 719 was regulated to introduce the hydrogengas into the chamber 701 so that the inside pressure of the chamber 701might reach up to 5×10⁻⁵ Torr.

A valve 727 of a bomb 708 to which argon gas (purity: 99.9999%) had beencharged was opened and regulated so that the reading of an outletpressure gauge 731 might indicate 1 kg/cm². Thereafter, an inflow valve712 was opened and further the outflow valve 720 was graudally opened toallow the argon gas to flow into the chamber 701. The outflow valve 720was gradually opened until the pressure gauge 725 indicated 5×10⁻⁴ Torr,and under that condition, the flow amount of the argon gas wasstabilized. Thereafter, the main valve 724 was gradually closed to bringthe inside pressure of the chamber 701 to 1×10⁻² Torr.

Subsequently, a valve 729 of a bomb 710 containing therein phosphine gas(purity: 99.9995%) was opened to regulate the outlet pressure so thatthe reading of an outlet pressure gauge 733 might indicate 1 kg/cm². Aninflow valve 714 was opened and an outflow valve 722 was graduallyopened and regulated while a flow meter 718 was observed, in order toadjust the flow amount of the phosphine gas to about 1.0% based on thatof the hydrogen gas indicated by the flow meter 715. After the flowmeters 715, 716 and 717 became stable, the high frequency power source734 was switched on to apply alternating power of 13.56 MHz, 1.6 KVbetween the target 705 and fixing member 703 thereby conducting thedischarge. Under that condition, the discharge was continued for 4 hoursto form an inner layer. Thereafter, the power source 734 was turned offto discontinue the discharging. Successively, the outflow valves 719,720 and 722 were closed while the main valve 724 was fully opened toevacuate the gas in the chamber 701 so that the vacuum degree wasadjusted to 5×10⁻⁷ Torr. Thereafter, similarly to the case of formingthe inner layer as mentioned in the foregoing, hydrogen gas and argongas were introduced into the chamber 701 and the main valve 724 wasregulated to bring the inside pressure of the chamber 701 to 2×10⁻²Torr.

Subsequently, a valve 728 of a bomb 709 containing therein diborane gas(purity: 99.9995%) was opened to adjust the reading of an outletpressure gauge 732 to 1 kg/cm². An inflow valve 713 was opened and theoutflow valve 721 was gradually opened. At that time, the outflow valve721 was regulated while the reading of a flow meter 717 was observed, inorder to control the flow amount of the diborane gas so that such flowamount might be about 1.0% based on the flow amount of the hydrogen gasindicated by the flow meter 715.

After the flow amount of hydrogen, argon and diborane gases becamestabilized, a high frequency power source 734 was switched on in orderto input a voltage of 1.6 KV, thereby causing a discharge. Under thatcondition, such discharge was continued for 40 minutes. Thereafter, thepower source 734 was turned off and the heater 704 was also switchedoff. When the substrate temperature reached 100° C. or below, theoutflow valves 715, 716 and 717 were closed, and further the subsidiaryvalve 723 was closed, while the main valve 724 was fully opened toevacuate the gas present in the chamber 701. The main valve 724 was thenclosed, and the leak valve 735 was opened to bring the inside pressureof the chamber 701 to the atmospheric pressure. Thereafter, thesubstrate 702 was taken out. In this case, the formed a-Si:H layer had atotal thickness of 8 microns.

The thus prepared image-forming member was used to conduct the sameimage-forming process as in Example 17 except that corona discharge with⊖6 KV was applied and a positively charged toner was used. As a result,a good image was obtained which was excellent in the resolution,gradation and image density.

EXAMPLE 19

An ITO (In₂ O₃ :SnO_(s) =20:1 shaped, burned at 600° C.) layer having athickness of 1200 angstroms was formed on one side surface of a glasssubstrate trade name: Corning 7059, supplied by Dow Corning Co.) havinga thickness of 1 mm and a size of 4×4 cm, both sides of which had beenpolished, in accordance with the electron beam vapor depositionprocedure. The obtained structure was heated in atmosphere of oxygen at500° C.

The structure was disposed in the fixing member 903 in the apparatusshown in FIG. 9 similar to that used in Example 17 so that the ITO layermight be faced upward. Subsequently, in accordance with the sameprocedure as in Example 17, the inside of the deposition chamber 901 forglow discharge was adjusted to a vacuum degree of 5×10⁻⁶ Torr and thesubstrate temperature was kept at 170° C., and thereafter the silane gasin the bomb 907 was allowed to flow into the chamber 901 so that theinside of the chamber 901 was brought to 0.8 Torr. A valve 923 of a bomb909 containing therein phosphine gas was opened to adjust the reading ofthe outlet pressure gauge 926 to 1 kg/cm². The inflow valve 915 wasopened and the outflow valve 918 was regulated while the flow meter 912was observed in order to control the flow amount of the phosphine gas sothat it might be 0.1% based on the flow amount of the silane gas. Undersuch condition, the phosphine gas was mixed with the silane gas andallowed to flow into the deposition chamber 901.

After the gas inflow become stable and the inside pressure of thechamber 901 was maintained at the constant level and further thesubstrate temperature was kept at 170° C., the high frequency powersource 905 was switched on to give rise to a glow discharge in a similarmanner to that in Example 17. This glow discharge was continued for 30minutes, and thereafter the high frequency power source 905 was turnedoff to discontinue the glow discharge, thereby completing the formationof an inner layer. The outflow valves 916 and 918 were closed, while thesubsidiary valve 919 and main valve 920 were fully opened to bring theinside of the chamber 901 to a vacuum degree of 5×10⁻⁶ Torr. Thesubsidiary valve 919 and main valve 920 were then closed. Next, theoutflow valve 916 was gradually opened and the subsidiary valve 919 andmain valve 920 were regulated to adjust the flow amount of the silanegas to the same flow amount as in case of forming the foregoing innerlayer. The power source 905 was switched on to cause a glow discharge,which was continued for 8 hours. Thereafter, the heater 904 and powersource 905 were turned off. After the substrate temperature wasdecreased to 100° C., the outflow valve 916 was closed, while the mainvalve 920 and subsidiary valve 919 were fully opened to bring the insideof the chamber 901 to 10⁻⁵ Torr or below. The subsidiary valve 919 andmain valve 920 were then closed and the inside of the chamber 901 wasbrought to atmospheric pressure by means of the leak valve 928. Thesubstrate was taken out which had an a-Si:H layer of about 11 microns intotal thickness.

The thus obtained image-forming member was tested with respect to theimage formation. The member was subjected to the image forming processcomprising corona charging with a voltage. Of ⊖6 KV, image exposureconducted from the back side and development with a positively chargeddeveloper. As a result, a good image was obtained with sufficientpracticality.

EXAMPLE 20

The same glass substrate as in Example 19, on which ITO was deposited,was used to form a structure similar to that finally obtained in Example19 in accordance with the same procedure and condition as in Example 19.

Subsequently, the inflow valve 915 and outflow valve 918 were closed.Heating by means of the heater 904 was maintained, while the highfrequency power source 905 was switched off. A valve 922 of a bomb 908which had been filled up with diborane gas was opened to adjust thepressure at an outlet pressure gauge 925 to 1 kg/cm². An inlet valve 914was gradually opened to allow the diborane gas to flow into a flow meter911. An outlet valve 917 was further gradually opened and regulated tocontrol the flow amount of the diborane gas so that the reading of theflow meter 911 might indicate 0.08% based on the flow amount of thesilane gas. Under that condition, the flow amount of the diborane gasinto the chamber 901 was stabilized along with the flow amount of thesilane gas. Succesively, the power source 905 was again switched on togive rise to a glow discharge. This glow discharge was maintained for 45minutes. Thereafter, the heater 904 and power source 905 were switchedoff. After the substrate temperature reached 100° C., the outflow valves916 and 917 were closed, while the main valve 920 was fully opened tobring the chamber 901 to 10⁻⁵ Torr or below. The subsidiary valve 919and main valve 920 were closed, and the inside of the chamber wasbrought to the atmospheric pressure by means of the leak valve 928. Thesubstrate was then taken out from the chamber. The thus formed a-Si:Hlayer was of about 12 microns in the total thickness.

The obtained image-forming member was used to carry out the same imageforming process as in Example 17 except that corona charging with ⊖6 KVwas effected and a positively charged developer was used. As a result, atoner image of an extremely good quality and a high contrast wasobtained on a transfer paper.

EXAMPLE 21

An MgF₂ layer having a thickness of 2,000 angstroms was formed on analuminum plate having a thickness of 0.1 mm and a size of 4×4 cm, thesurface of which had been polished with a buff into a surface like amirror surface and cleaned, in accordance with the electron beamdeposition. This structure was used as a substrate. The substrate wassecurely placed on the fixing member 903 in the apparatus shown in FIG.9 similarly to Example 17 so that the MgF₂ layer might be faced upward.

In accordance with the procedure as in Example 17, the depositionchamber 901 for glow discharge and all gas conduits were brought to avacuum degree of 5×10⁻⁶ Torr and the substrate temperature was kept at220° C. The silane gas was allowed to flow into the chamber 901 from thebomb 907 in the same manner as in Example 17 to bring the insidepressure of the chamber 901 to 1.0 Torr. After the flow amount of thesilane gas and the substrate temperature became stabilized, the highfrequency power source 905 was switched on so that a glow dischargestarted. Under this condition, the glow discharge was continued for 5hours. Thereafter, the power source 905 was switched off to discontinuethe glow discharge. Successively, the valves 923, 915, 918 were openedand regulated with the reading of the flow meter 912 being carefullyobserved, in order to control the flow amount of the phosphine gas fromthe bomb 909 so that it might be 0.05% based on the flow amount of thesilane gas. The phosphine gas was then introduced into the chamber 901with its stabilized flow amount. The high frequency power source 905 wasagain switched on to give rise to a glow discharge. During the glowdischarge, the outflow valve 918 was gradually opened so that the flowamount of the phosphine gas based on that of the silane gas might beincreased to 0.06% from the initial amount, i.e., 0.05% for about 10minutes, and the glow discharge was continued for one hour. Thereafter,the power source 905 and heater 904 were switched off. After thesubstrate temperature was decreased to 100° C. or below, the outflowvalves 916 and 918 were closed. The main valve 920 was then fully openedto bring the chamber 901 to 10⁻⁵ Torr or below. The subsidiary valve 919and main valve 920 were closed, while the leak valve 928 was opened tobring the chamber 901 to the atmospheric pressure. The substrate wastaken out from the chamber. The thus formed a-Si:H layer had a totalthickness of about 7.5 microns.

The thus obtained image-forming member was subjected to the same imageforming process as in Example 17 except that positive corona chargingwas conducted with ⊕6 KV and a negatively charged developer was used. Asa result, an extremely good image was obtained.

The image-forming member was fixed to a drum for photosensitive member,i.e. an aluminum drum having no photosensitive layer of a commerciallyavailable copying machine (trade name: NP-L7, supplied by CANON K.K., apartially modified test machine) and subjected to the image-formingprocess comprising charging with ⊕6 KV, image exposing, developing withnegatively charged liquid developer, liquid-squeezing simultaneous withnegative charging, and transferring simultaneous with positive charging.As a result, a good image was obtained on a plain paper. In addition,even when such image-forming process was repeated continuously 100,000times, the quality of the obtained images remained unchanged.

EXAMPLE 22

An aluminum substrate having a thickness of 0.1 mm and a size of 4×4 cm,the surface of which had been cleaned, was disposed on the fixing member903 in the apparatus shown in FIG. 9 similarly to the case of Example17. In accordance with the same procedure as in Example 17, the air inthe deposition chamber 901 and gas conduit was evacuated to bring themto a vacuum degree 5×10⁻⁶ Torr, and the substrate was kept at 250° C.The silane gas was allowed to flow into the chamber 901 according to thevalve operation of Example 17 so that the inside pressure of the chamber901 was adjusted to 0.3 Torr.

The valve 922 of the bomb 908 which had been filled up with diborane gaswas opened to adjust the reading of the outlet pressure gauge 925 to 1Kg/cm². The inflow valve 914 was gradually opened and also the outflowvalve 917 was gradually opened so that the reading of the flow meter 911might indicate 0.15% based on the flow amount of the silane gas. Thus,the diborane gas was allowed to flow into the chamber 901. After theflow amount of the silane gas and diborane gas became stabilized and thesubstrate temperature was stabilized at 250° C., the power source 905was switched on to cause a glow discharge. Under the same conditions,the glow discharge was conducted for 30 minutes and continued. Theoutflow valve 917 for the diborane gas was gradually closed andregulated while the flow meter 911 was observed, in order to control theflow amount of the diborane gas so that such flow amount might be 0.05%based on that of the silane gas. Under this condition, the glowdischarge was further continued for 6 hours. Thereafter, the outflowvalves 916 and 917 were closed so that the inside of the chamber 901 wasadjusted to a vacuum degree of 5×10⁻⁶ Torr. Successively, the silane gaswas allowed to flow into the chamber 901 in the same manner so that thechamber 901 was brought to 0.3 Torr. The valve 923 of the bomb 909 towhich phosphine gas had been charged was opened to adjust the outletpressure to 1 Kg/cm², and the inflow valve 915 and outflow valve 918were gradually opened and regulated while the flow meter 912 wasobserved, in order to adjust the flow amount of the phosphine gas to0.08% based on that of the silane gas. The phosphine gas was mixed withthe silane gas and allowed to flow into the chamber 901. After the gasflow became stabilized, the power source 905 was switched on to giverise to a glow discharge. The glow discharge was continued for 45minutes. Thereafter, the power source 905 and heater 904 were switchedoff. After the substrate temperature reached 100° C., the outflow valves916 and 918 were both closed, while the main valve 920 was fully openedto bring the chamber 901 to 10⁻⁵ Torr or below. The subsidiary valve 919and main valve 920 were closed, and the leak valve was opened to bringthe chamber 901 to the atmospheric pressure. The substrate was thentaken out. The formed a-Si:H layer had a total thickness of about 9microns.

The back side, i.e., the aluminum surface of the thus obtained structurewas brought into close contact with an adhesive tape and then immersedperpendicularly into a 30% solution of polycarbonate resin in toluene.The structure was drawn up at a speed of 1.5 cm/sec. so that apolycarbonate resin layer having a thickness of 15 microns was formed onthe a-Si:H layer. Thereafter, the adhesive tape was removed.

The thus obtained image-forming member was fixed to a drum for aphotosensitive member, i.e. an aluminum drum having no photosensitivelayer of a commercially available copying machine (trade name: NP-L7,supplied by CANON K.K., a partially modified test machine) and subjectedto the image-forming process comprising the primary charging with ⊕7 KV,image exposing simultaneous with AC charging with 6 KV, developing witha negatively charged liquid developer, liquid-squeezing (rollersqueezing) and transferring simultaneous with charging with ⊕5 KV. As aresult, a sharp image of a high contrast was obtained on a plain paper.Even when the process was continuously repeated, 100,000 times, theobtained images retained the initial excellent image quality.

What we claim is:
 1. A process of preparing an electrophotographic imageforming member comprising a substrate for electrophotography and ahydrogenated amorphous silicon layer being sensitive to electromagneticwaves and comprising two layer regions each having different electricproperties, said process comprising depositing on said substrate saidtwo layer regions by electric discharge decomposition of at least onegaseous material containing silicon and hydrogen and at least oneelement selected from Group III or V of the Periodic Table and, duringdeposition, incorporating in one of said two layer regions thereof atleast silicon and hydrogen and the other layer region at least silicon,hydrogen and at least one element in Group III or V of the PeriodicTable, so that the depletion layer is formed between said two layerregions.
 2. A process according to claim 1, wherein the element isselected from the group consisting of B, Al, Ga, In, Tl, N, P, As, Sband Bi.
 3. A process according to claim 1, wherein the gaseous materialcontaining silicon is selected from the group consisting of SiH₄, Si₂ H₆and Si₄ H₁₀.
 4. A process according to claim 1, wherein the gaseousmaterial containing the element is selected from the group consisting ofPH₃, P₂ H₄ and B₂ H₆.
 5. A process according to claim 1, wherein thesubstrate is maintained at a temperature within the range from 50° to350° C. during deposition.
 6. A process according to claim 1, whereinthe electric discharge is caused with an electric current density of 0.510 mA/cm² and a voltage of 100-5000 V.
 7. A process according to claim1, wherein the hydrogenated amorphous silicon is deposited at adeposition range of 0.5-100 A/sec.